Physiology of the

central nervous system

Motor division of the CNS

Reflex

General function of the nervous system (NS)

Nervous system

- communication network of neurons

- allows interaction with the external and internal

environment

• sensory division – receiving input

• information processing

• motor systems - output

• main function: regulation, coordinationa and

integration of body functions

• purpose: adaptation to changes - maintenance

of homeostasis and survival

http://www.alz.org/braintour/images/neuron_forest.jpg

1. Peripheral NS

2. Central nervous system

• Spinal cord

- conducts sensory information to the brain

- conducts motor information to the effector organs

- serves as a simple regulatory centre (reflexes)

- damage of the spinal cord breaks down the connection between

periphery and higher centres – serious consequences

• Brain

- subcortical level - control of involuntary and

subconscious functions

- brain cortex

- control of voluntary functions

- control of lower levels of CNS

- site of cognitive (higher) functions:

memory, learning, thinking

Levels of the CNS

Peripheral nervous system (PNS)

- transmits information from periphery to the central

nervous system and vice versa

Includes

- cranial nerves – originate in brain (I – XII)

- spinal nerves - originate in spinal cord

(C1, C2...Th,..L, S..)

Components

A. afferent (sensory) nervous system (incoming to CNS)

B. efferent (motor) nervous system (outgoing from CNS)

a. somatic nervous system (transmit impulses to skeletal muscle)

b. autonomic nervous system (transmit impulses to smooth muscles, cardiac muscle and glands)

I. sympathetic division (fight or flight)

II. parasympathetic division (rest and repair)

Motor functions and their regulation

Brain cortex – motor areas (primary, premotor, supple-

mentary motor) decision about voluntary movements

Basal ganglia

- regulation of well co-ordinated voluntary movements

- cognitive control of voluntary movements (e.g. running

away from a dangerous animal)

Cerebellum

- making movements „smooth“

- precisely regulates the sequence and duration of the

elementary movements of each of these segments

Brainstem

– posture control, hand and eye movements

Spinal reflexes

- simple movements – reflex movements

Reflex Voluntary Rhythmic

- quick, predictable

(stereotyped),

involuntary response

to stimulus

- triggered by a stimulus

- purposeful, goal-

drected movement

- often learned

movements, improve

with practice

-combines characteristics of

reflexes with voluntary

movement (initiation,

termination)

-once initiated, the

sequence of relatively

stereotyped repetitive

movements can continue in

automatic manner

e.g. knee jerk e.g. writing text into a

notebook

e.g. walking, chewing

Spinal control Cortical control Initiate by central pattern

generators (m. oblongata)

Least complex Most complex Intermediate complexity

Somatic motor system – 3 types of movements

Knee jerk – the patellar reflex

- tap on the tendon of m. quadriceps femoris

- the leg makes a „kick“ (extension in knee joint occurs)

Reflex

• definition: predictable, quick, stereotyped and involuntary response to stimulus

• action that results from passing a nerve impulse over a reflex arc

• „lowest level“ of regulation of motor functions

Reflex arc – the basic circuit that

underlies a reflex:

1. sensory receptor – gathers

stimuli

2. afferent nervous fibre – signal

transduction into CNS

3. reflex (integration) centre –

processes information

4. efferent nerve fibre –

transduction of response

5. effector (muscle, gland)–

performance, response to the

stimulus A reflex arc

Classification of reflexes – with respect to:

A/ Count of synapses:1. Monosynaptic - 1 synapse in the reflex arc

2. Polysynaptic= 2 or more synapses in reflex arc

https://s-media-cache-ak0.pinimg.com/originals/a6/41/3f/a6413f649558834e5541fb7e03124f54.jpg

Classification of reflexes – with respect to:

B/ Type of sensory receptor

Exteroceptive – receptor in the reflex arc is an exteroceptor (gathers stimuli from

external environment)

Proprioceptive – receptor in the reflex arc is an proprioceptor (gathers stimuli

about position of the body)

Interoceptive – receptor in the reflex arc is an proprioceptor (gather stimuli from

internal environment)

C/ Integration (reflex) centre Cranial – centre in nuclei of the cranial nervesSpinal – centre in the spinal cordExtracentral – centre in autonomic ganglia

D/ EffectorSomatic – effector: skeletal muscleAutonomic (visceral) – effector: cardiac muscle, smooth muscle, gland

E/ OriginInborn – related to locomotion, defence, food intake, sexual behaviourAcquired – develop during life

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Spinal reflexes

Spinal reflexes

- integration centre in the spinal cord

- include - the muscle stretch reflex

- the Golgi tendon reflex

- the crossed extensor reflex

- the withdrawal reflex

• involved in regulation of movement, muscle tone and posture

– motor control (subcionscious level)

• both receptor and effector are in the same muscle

• types of sensory receptors involved in

spinal reflexes:

– a muscle spindle

– Golgi tendon organs

Muscle stretch reflexes (proprioceptive)

• monosynaptic

• spinal or cranial reflex – reflex centre in the spinal cord or nuclei of the cranial

nerves

• example: knee jerk

• a stretch receptor in a muscle

• a bundle of modified muscle fibres encased

in a capsule

Polar parts of the muscle spindle

- composed of intrafusal fibres that are

contractile (can respond to a stimulation by

contraction)

Central part of the muscle spindle

- fibres non contractile – do not respond to

stimulation by a contraction

- can be passively stretched

- a sensory nerve is wrapped around the fibres

The muscle spindle

• adequate stimulus for the muscle spindle:

muscle stretch(by tapping with the reflex hammer on the muscle

tendon tendon and also the muscle are stretched!!)

• by the stretch both central and polar parts are

prolonged

• prolongation of the central part triggers receptor

potential in the sensory nerve wrapped around

• action potential is triggered and transmitted

via the sensory nerve to the reflex centre

• response – contraction of the extrafusal

muscle fibres of the same muscle

rest

PolarPolar Central

The muscle spindle

• tapping on the muscle tendon passive prolongation of the muscle

spindle=stimulus (1)

• action potential is transmitted by afferent sensory fibre (2)

• afferent fibre enters spinal cord through posterior roots

• afferent fibre synapses in the anterior horn with a – motoneuron

• synapse in different parts of the spinal cord (C, Th, L, S) = integration centre (3)

• action potential is transmitted by efferent fibre (a – motoneuron)

into muscles (via the motor endplate) (4)

• muscle contraction occurs (5-response) - this is seen as movement

Spinal muscle stretch reflex - reflex arc - summary

• a proprioceptive sensory receptor

• located at the insertion of skeletal muscle

fibers into the tendons of skeletal muscle

• made up of strands of collagen connected

at one end to the muscle and at the other

with the tendon

• when the muscle contracts, the collagen

fibrils are pulled tight, and this activates the

Golgi tendon organ afferent

• it detects tension of the muscle

Golgi tendon organ

• receptor: Golgi tendon organ

• stimuli (sensitive only to very strong stimuli)

- muscle contraction

- passive stretch of the muscle

• signal transmitted via afferent nerve fibre

and by interneurons (inhibitory) in spinal

cord to alpha motorneurons

• inhibition of alpha motoneuron!!!

• response: muscle relaxation (the same

muscle where the receptor is located)

• function: protection against rupture of the

muscle

The Golgi tendon reflex (inverse myotatic reflex, polysynaptic)

https://d1yboe6750e2cu.cloudfront.net/i/217f697b124975ecae635be08e16eae083cec19d

• stimulus causes response in both flexors and extensors of the same side:

1. activation of alpha motoneurons of the ipsilateral flexor muscles,

2. at the same time inhibits alpha motoneurons that supply antagonistic

extensor muscles

• example: when touching a hot object – contraction of flexors and relaxation of extensors

causes removing the hand

Withdrawal reflex (polysynaptic)

• a stimulus causes response on both sides in both

extensors and flexors:

1.activation of alpha motoneurons of the

ipsilateral flexor muscles

2.inhibits alpha motoneurons that supply

antagonistic extensor muscles

- the opposite pattern occurs on contralateral

side

3.flexors are inhibited

4.extensors are stimulated

• example: when a person steps on a nail, the leg that is

stepping on the nail pulls away, while the other leg takes

the weight of the whole body- reflex enhances postural

support

• example: locomotor pattern generator

Crossed extension reflex – polysynaptic

Spinal cord

• segmental organization

• segments (levels) of the spinal cord contain

regulatory circuits involved in control of the

movements of a particular region of the body

• muscle stretch reflexes have their inegration

centres in different segments of the spinal cord

Muscles in axial parts of the body limbs

(a motoneurons medial part) (a motoneurons -lateral part)

= somatotopic organization

Examination of reflexes in a human

• basic examination in neurology

• indicates the function of reflex arc (and all its components)

• reflex - stereotypic reaction = predicted response

• normoreflexia – normal reflex response on a stimulus

• abnormal response indicates disorder in a part of reflex arc

Types of abnormal results:

• hyperreflexia (or clonus) – hyperactive reflex

• hyporeflexia – diminished reflex

• areflexia – absence of response

• abnormal reflex – the response on the stimulation is abnormal

Principle

• sensory receptors are stimulated

• the reflex response on stimulation is observed and evaluated

Procedure

• the patient is in sitting or lying position (depends on the reflex)

• sensory receptors are stimulated by a reflex hammer, cotton,

light, needle (depends on the reflex that we want to examine)

• examine following reflexes (see next slides)

Task: Examination of reflexes in a human

Reflex examination video

https://www.youtube.com/watch?v=eqOpNQH09pA

Proprioceptive (deep tendon) reflexes- sensory receptor – in muscle, tendon

• Masseter reflex (n V)

S: tap on a spatula put on the

lower jaw

(mouth is moderately open)

R: closing the mouth

• Naso-palpebral reflex (n V,VII)

S: tap on the nasal base

R: closing of eyelids

• Biceps reflex (C5)

S: tap on lacerus fibrosus m. bic. brachii

R: flexion of the forearm

• Triceps reflex (C7)

S: tap on olecranon ulnae

R: extension of the forearm

• Styloradial (brachioradial)reflex (C7)

S: tap on proc. styloideus radii

R: flexion of forearm

• Patellar reflex (knee jerk, L 2-4)

S: tap on the tendon of m. quadriceps

femoris

R: extension in knee joint

- the patient is sitting, and the examined

limb is put over the knee of the other

- if no response occurs, do the Jendrassik

manoeuver (abduce one hand from

another)

• Achilles tendon reflex (ankle jerk,

L5-S2)

S: tap on Achilles tendon

R: extension of the foot

- the patient may lie or kneel

Achilles tendon reflex measurement

and the thyroid function

Principle:

- thyroid hormones (thyroxin, triiodthyronine)

influence the activity of the central nervous

system

- examination of Achilles tendon reflex - an indirect

indicator of thyroid activity – suitable for screening

(also other reflexes can used)

- reflex response is directly influenced by the level

of thyroid hormones

• normal reflex response – euthyrosis

• delayed response – hypothyrosis

• excessive response – hyperthyrosis

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Exteroceptive reflexes

- sensory receptors in skin or mucosa

Corneal reflex (n V, VII)

S: touching the cornea with a piece of cotton

R: blinking

(used in surgery-depth of anaesthesia in the

veterinary medicine, is the last to disappear in

deepening anesthesia)

Abdominal reflexes (Th 5 – Th 11)

• epigastric

• mesogastric

• hypogastric

S: drawing of the abdominal wall with a

needle

R: muscle contraction (lying position)

Plantar reflex (L5-S2)

S: stimulation of external side of planta pedis with a needle (from heel to little

finger and other fingers)

R: plantar flexion or the toe (or all fingers)

- if pyramidal pathway is impaired the response in plantar reflex is abnormal

(this is called Babinski phenomenon)

R: extension of the toe

- normal in babies up to 6-8 months, later a sign of disorder

- indicates abnormalities in pyramidal tract

https://i.pinimg.com/originals/27/58/07/27580

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Autonomic (vegetative) reflexes- response – transmitted by autonomic fibres

• Pupilary light reflex

S: illumination of an eye (use battery)

R: miosis – diameter of the pupil becomes narrow

- consensual reaction – if one eye is illuminated,

miosis occur bilaterally

• Oculocardial reflex

S: moderate pressure on the eyeball

R: decrease in pulse frequency (by 5-10 beats per minute)

• Orthostatic reflex

S: sudden change position from lying to sitting

R: increase in pulse frequency

• Solar reflex

S: pressure against solar plexus

R: drop in pulse frequency

– all reflexes- measure heart rate only 15´´, then multiply by 4 (rate per min)

Neurons of the spinal grey matter

a motor neurons

- their axons leave via ventral roots (and cranial nerves) and terminate in muscles on the motor end-plate

- discharge of a a-motor neurons causes a skeletal muscle contraction

- receive input from descending neurons of pyramidal pathway (= tr. corticospinalis)

g motor neurons

- innervate muscle fibres of the muscle spindles (intrafusal muscle fibres)

- receive input from decending neurons

of extrapyramidal pathways

- involved in control of the muscle tone

interneurons

propriospinal neurons

- short fibres,

- synapse within the spinal cord

- vertical connections

extrapyramidal pyramidal

g

a

Gamma fibres and the muscle spindle

• stimulation of the muscle via g - fibres causes

contraction of intrafusal fibres in both polar

regions (periphery) of the muscle spindle

• thus, the equatorial region of the muscle

spindle becomes prolongedGamma

fibre

rest

Receptor potential of a muscle spindle can be elicited by:

1. Passive stretch (e.g. tapping with the reflex hammer)

– passive prolongation of the central part

2. Active stretch

• by stimulation via g - fibres

• the g - fibres terminate in the polar parts of muscle spindle

Gamma

fibre

Alpha-gamma loop

extrapyramidal

1. stimulation of the muscle via g - fibres

causes contraction of intrafusal fibres in

both polar regions (periphery) of the

muscle spindle

2. thus, the equatorial region of the muscle

spindle becomes prolonged

= stimulus – elicits a muscle stretch reflex

3. receptor potential is elicited in the muscle

spindle – travels via afferent fibre to the

reflex centre in the spinal cord

4. synapse with a – motor neuron

5. response - contraction of the extrafusal

muscle fibres

g

a

1 2

3

4

5

Alpha-gamma co - activation

• a loop for regulation of the muscle tone

• a and g motor-neurons are activated together during most movements

• command signal from the brain activates simultaneously a motoneurons (pyramidal

pathway) and g motor-neurons (extrapyramidal pathway) = a - g coactivation

• the ultimate result of a and g co-activation is to adjust the muscle tone to the

demands in order to allow for a precise movement

extrapyramidal pyramidal

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Monosynaptic reflex arc

Autonomic reflex arc (efferent pathway – 2 neurons – connected in ganglia)

The cerebellum is important in balance and in

planning and executing voluntary movement

Cerebellum

• control if the executed movement matches the planned movement

• an important control center for motor function, regulates movements´

– rate

– range

– force

– direction of the movements

1. vestibulocerebellum (archicerebellum)

- regulates balance and eye movements

2. spinocerebellum (paleocerebellum)

- regulates synergy of the body and limb movements + is able to elaborate

proprioceptive input in order to anticipate the future position of the body

3. cerebrocerebellum (neocerebellum)

- involved in planning and initiation of movements

Examination of the cerebellum

Scanning speech

• Scanning speech refers to slow, slurred, monotonous, and irregular

speech that is associated with dysarthria due to oral motor ataxia.

Causes enunciation of individual syllables.

• Test: Ask the patient to say: “the British parliament”. In case of

scanning speech it becomes “the Brit-tish Par-la-ment.”

Nystagmus

• Ocular findings are generally less prominent, but ipsilateral gaze-

evoked nystagmus are is seen with fast phase toward side of cerebellar

lesion.

• Test: Ask the patient to follow your finger

and observe presence of nystagmus.

http://stanfordmedicine25.stanford.edu/the25/cerebellar.html

Dysmetria (Finger to nose & finger to finger test)

• Limb ataxia is usually seen clinically as difficulty with

coordinated tasks.

• Test:

• or ask to touch their nose then fully extend to touch your finger

• increase the difficulty by moving your finger to different

locations

Rebound phenomenon

• the patient pulls on your hand and when you slip your hand out

of their grasp, normally the antagonist muscles will contract and

stop their arm from moving in the desired direction.

• In cerebellar disease this response is completely absent

causing to limb to continue moving in the desired direction.

• Test: Have the patient pull on your hand and when they do, slip

your hand out of their grasp. Observe the presence of rebound

phenomenon.

Rapid alternating movements

• Common finding in cerebellar disease is dysdiadochokinesia

(incoordination when performing rapid alternating

movements).

• Test: Ask patient to place one hand over the next and have

them flip one hand back and forth (pronate and supinate) as

fast as possible (alternatively you can ask the patient to

quickly tap their foot on the floor as fast as possible).

Hypotonia

• Low muscle tone may be present in cerebellar diesases.

• Test: Perform the examination of the patellar reflex (knee

jerk). “Pendular” knee jerk, leg keeps swinging after knee

jerk more than 4 times (4 or less is normal).

Gait

• Test: Ask the patient to walk straight forward

• In cerebellar disorders – the gait is commonly wide

based and staggering. They may fall to the side of the

lesion.

Romberg’s test

• Whilst Rombergs test does not directly test for cerebellar

ataxia, it helps to differentiate cerebellar ataxia from

sensory ataxia. In cerebellar ataxia the patient is likely to

be unsteady on their feet even with the eyes open.

• Test: Perform Romberg’s test by asking the patient to

stand unaided with their eyes closed and heels together.

• If the patient sways (titubation) or loses balance then

this test is positive. Stand near the patient in case they

fall.

Regulation of the motor functions – Brain cortex

• Primary motor cortex - precentral gyrus in the frontal lobe

– Large neurons (pyramidal cells) allow conscious control of movement of individual

skeletal muscles

– The pyramidal cells' long axons form pyramidal (corticospinal) tracts

– Motor areas have been spatially mapped = somatotropy (motor homunculus)

• Premotor cortex - anterior to the precentral gyrus in the frontal lobe

– Regions controls learned motor skills that are repeated or patterned

– Also coordinates the movements of several muscles simultaneously and\or

sequentially by sending activating

impulses to the primary motor cortex

• Broca's area - anterior to the premotor area

– Involved in directing motor speech

• Frontal eye field - anterior to the

premotor cortex and superior

to Broca's area

– Controls voluntary movement of eyes.

Volunary movement

• Multiple association areas of the cerebral cortex

- motivation, ideas to produce motor activity

• Supplementary and premotor cortex

– development of a motor plan

– Identification of the specific muscles that need to contract and their sequence

• Primary cortex cortex

- upper motorneurons

• Spinal cord

• Lower motorneurons

Motor homunculus

At the primary motor cortex, motor representation of the body is arranged in an orderly manner.

The amount of cortex devoted to any given body region is proportional to how richly innervated

that region is (not to the body region's physical size).

Areas of the body with greater or more complex motor connections are represented as larger in

the homunculus, the resulting image is that of a distorted human body, with disproportionately

huge hands, lips, and face.

Lateralization of brain functions

Old concept

-Left hemisphere is dominant because it controls the dominant hand

Current concept- generally, each hemisphere's structure is mirrored by the other side- despite strong similarities, the functions of each hemisphere differ

Left hemisphere functions- verbal functions: speech,

reading, writing

- langue – grammar, spelling

- mathematics – analytical

thinking, counting and

measurement

- logical thinking

- complex voluntary motor

functions

- sequential approach

Right hemisphere functions- complex sensory perception (music, dance)

- site of spatial abilities

- fantasy, art

- visual memory - face recognition

- language – intonation, accentuation

- simultaneous, holistic approach

Males

– exhibit more lateralization

Females

– more bilateral

Task: Assessment of motor handedness

• handedness - the preference of one hand over the other

• usually one hand is considered dominant

• most people are right-handed (90% of population)

• some individuals exhibit the ability to use both hands equally (ambidexterity)

• preference for one hand is most likely the effect of brain lateralization

• handedness has a genetic basis, it is also influenced by socio-cultural pressures

http://www.well.ox.ac.uk/_asset/image/nov-10-handedness-and-language.jpeg/fit/460/768

- read the inventory questions and respond to each by filling a number into the box

Please mark the box that best describes which hand

you use for the activity in question

Always

Left (-50)

Usually

Left (-25)

No

Preference (0)

Usually

Right (25)

Always

Right (50)

Writing (a letter)

Throwing (a ball)

Scissors

Toothbrush

Knife (without fork)

Spoon

Match (when striking)

Computer mouse

Result:

- by making a sum of all numbers you get a score of Laterality Quotient (LQ)

- evaluation: righthanded LQ: +400 to +200

lefthanded LQ: -400 to -200,

mixed handedness LQ: -200 to +200.

Conclusion: Comment on your motor hand preference:

Always

Left (-50)

Usually

Left (-25)

No

Preference

(0)

Usually

Right (25)

Always

Right (50)

Writing (a letter)

Throwing (a ball)

Scissors

Toothbrush

Knife (without fork)

Spoon

Match (when striking)

Computer mouse