Central Nervous System

Dr. AndersonGCIT

Animal Body Plans

Cephalization

• Organisms that have a proper and distinct “head end”

• Why is this important?

Cephalization

Major Divisions

• Brain – Processes information coming in from afferent

nerves– Sends signals (motor) out to body via spinal cord

and cranial nerves

• Spinal Cord – Connects brain to peripheral nerves– May also initiate motor responses (reflexes)

Brain Divisions - Anatomical

• Cerebrum (Cerebral Hemispheres)• Diencephalon• Brain Stem (Pons, midbrain, medulla)• Cerebellum

Each of these divisions can be divided further, into anatomical AND functional divisions

Brain Ventricles

• “Spaces” in the brain that are left over from embryonic brain development

• Spaces are filled with cerebro-spinal fluid

• Why?

Hydrocephaly

• “Water on the brain”

• Pressure inside the brain inceases due to too much cerebro-spinal fluid (CSF) being produced or drainage is blocked

Functional Anatomy

Major Brain Divisions

Cerebrum

Cerebrum

• Divided into hemispheres bilaterally

• Each half of the cerebrum is further divided into regions by:– Gyri “Twisters”– Sulci “shallow grooves”– Fissures “Deeper grooves”

Major Fissures

Longitudinal Fissure Transverse cerebral fissure

Major Sulci and Gyri

Brain and SkullFrontal lobes lie within the anterior cranial fossa

The anterior parts of the temporal lobes lie within the middle cranial fossa

The posterior cranial fossa houses the brain stem and cerebellum

Cerebral Cortex• Only 2-4 mm thick, but 40% of brain mass

• Contains BILLIONS of neurons (convolutions increase surface area)

• Functional areas can be identified, but all areas of the cortex are interconnected

• Each hemisphere is associated with the opposite side of the body (laterally)

Stroke

• People that have motor areas affected on only one side of their brain

• Opposite part of the body may be paralyzed

Cortex – Thin Shell of Grey Matter

Functional Cortex Areas

• Motor – initiates movement in areas of the body

• Sensory – Sensations from the body come here to be processed

• Association Areas – where incoming information from the body is processed

Motor and Sensory Areas

Primary Motor Cortex

• Located in the pre-central gyrus

• Pyramidal cells – allow conscious control and coordination of voluntary movements– Connect to spinal cord (pyramidal tracts)

• Motor areas are not simply discrete, but interconnected!

Premotor Cortex

• Anterior to precentral gyrus

• Provides a ‘memory bank’ for skilled motor activities

• Also controls motor activity that rely on sensory feedback

Outline the Primary and Premotor Cortices

Broca’s Areas

• Control the muscles that are responsible for speech

• Also active during “planning” of motor activities

• Would you expect this area to be smaller or larger in chimps (our closest animal relative)?

Outline Broca’s Areas

Frontal Eye Field

• Lies anterior (and within) premotor cortex

• Controls voluntary movements of the eyes

Sensory Areas – Primary Somatosensory cortex

• Post-central gyrus of the parietal lobe

• Neural input from the skin and proprioreceptors (from muscles and joints) is decoded and the stimulated body part is identified (spatial discrimination)

Somatosensory Association Cortex

• Integrates sensory inputs to produce an understanding of what is being felt

• DEMO

• What would damage to this area do?

Label the Primary and Association Somatosensory Cortices

Primary Visual Cortex

• Receives input from the cells in the retina of the eye

Visual Association Cortex

• Uses past visual stimuli “visual memories” to determine what is being seen

• Uses different aspects of the visual data (shape, contrast, depth perception, etc.)

Primary Auditory Cortex

• Superior margin of temporal lobe

• Gathers data on pitch, loudness and location (by the difference in impulses received by each ear)

• Auditory Association Area – interprets sound by relating to past auditory memories

Olfactory Cortex

• On medial aspect of temporal lobe

• Part of the old “rhinencephalon” (nose brain) that still exists– Most of the rest of our ancestral rhinencephalon

has evolved to process “higher” emotions – the limbic system

Auditory and Olfactory Cortices

Insula

• Part of the cerebral cortex that is just deep to the temporal and frontal lobes

• Seen when temporal lobe is retracted

Other Cortices

• Gustatory Cortex - Perceives taste stimuli– Just deep to temporal lobe (on the insula)

• Visceral Cortex – Perceives information from the gut– Just posterior to gustatory cortex

• Vestibular Cortex – provides information about the position of the head in space– Posterior of insula

Multimodal Association Areas

• Generally receives information after being processed by the association cortices for each sense

• Receives input from multiple stimuli, and– Give meaning to it– Devote it to memory– Act upon it – Relate it to previous experience– Senses related to conciousness

Motor Homonculus (cortical)

Somatosensory Homonculus

Anterior Association Area

• In frontal lobe

• Center for– Intellect– Personality– Judgement– Planning– Abstract Ideas

Posterior Association Area• Temporal, parietal,

occipital lobes

• Allows to recognize:– Patterns and faces– Localizing yourself in

space– Self-awareness

Limbic Association Area• Includes the singulate gyrus, hippocampus– Provides emotional impact that is tied to certain

situations

– Example?

Lateralization

• Each hemisphere of the brain is functionally identical

• However, each hemisphere is considered to be functionally different (slightly) in higher brain functions, but research continues– “Left-brain” – math, logic, language– “Right-brain”- art, music, creativity

Cerebral White Matter

• Deep to the cortex

• Connects “grey matter” cortices to each other and to the lower CNS (spinal cord)

• White color is due to the myelination of the fibers composing the tissue

Grey and White Matter Distribution

White Matter Fibers

• Commissures – Connect corresponding grey matter of the two brain hemispheres– Allows them to act together

• Association Fibers – Connect different parts of the same hemisphere

• Projection Fibers – connect the brain to the rest of the nervous system (spinal cord)

Diencephalon

• Forms the core of the forebrain (surrounded by cerebral hemispheres)

• 3 major divisions– Thalamus– Hypothalamus– Epithalamus

Thalamus• Consists of 2 bilateral

egg-shaped “nuclei”

• Serves as a relay station for all impulses entering the brain– All afferent impulses are

directed to the relevant areas of the brain

– All efferent impulses are directed to the relevant areas of the body

Hypothalamus

• Located inferior to the thalamus

• The main visceral control center of the body, maintains homeostasis

Hypothalamus Functions

• Autonomic control center – Heart rate, blood pressure, digestive tract

movements, etc.• Emotional Responses– Pleasure, fear, rage, sex drive

• Body Temperature– Fever, sweating, shivering,

Hypothalamus Functions (con’d)

• Food intake– Monitors glucose levels in the blood

• Water balance and thirst– Monitors levels of solute concentrations in the

blood• Sleep-wake cycles• Major controller of the endocrine system

Epithalamus

• Most dorsal portion of the diencephalon

• Most notably contains the pineal gland, which secretes the hormone melatonin– Helps regulate the

sleep-wake cycle

Brain Stem

• Directly inferior to diencephalon

• Three major areas– Midbrain– Pons– Medulla Oblongata

Midbrain• Function– Fight-or-flight response– Visual reflex centers (visual

tracking)– Startle reflex

Pons

• Helps to maintain the normal rhythm of breathing

• Serves as a bridge between the motor cortex and the cerebellum

Medulla Oblongata

• Located just in the opening of the foramen magnum (top of spinal cord)

• Regulates many homeostatic functions– Cardiovascular regulation– Respiratory rhythm – Hiccuping, coughing, vomiting, swallowing,

sneezing

Cerebellum• Bilaterally

symmetrical organ that occurs inferiorly to the occipital lobe

• Times our efferent motor impulses, resulting in smooth coordinated movements

Cerebellar Processing

1. Cerebral motor areas relay their intent to start voluntary muscle contraction

2. Afferent impulses from proprioreceptors send information about body position and momentum

3. Cerebellar cortex calculates the amount and direction of muscle contraction needed to complete the action

4. The “plan” of motion is sent back to the motor areas of the cerebrum, where impulses are sent for the action to be executed

The Limbic System• Our “emotional” brain

• Composed of organs that surround the upper brain stem– Rhinencephalon– Cingulate gyrus– Amygdala – Hypothalamus– Fornix

Emotional Brain• Amygdala– Recognizes fearful facial

expressions– Core of the fear

response

• Cingulate gyrus– Helps to express

emotions as gestures– Resolves mental

conflicts

Crossed Communication

• Even Numbers• The limbic system communicates directly with the frontal

lobe via white matter.

• Odd Numbers• Most limbic system actions are regulates by the

hypothalamus

• What issues might these connections cause??

The Reticular Activating System

• The reticular neural formation extends from the brain stem into many major areas of the brain– Makes this system ideal for arousing the brain as a

whole

• The RAS filters out “typical” stimuli, but arouses the brain when something unusual or significant happens

Levels of Consciousness

Alert Drowsy/Lethargic Stupor Coma

What causes us to shift along this continuum?

Memory• The storage and retrieval of information

• Memories are stored in parts of the brain that need them (e.g. visual association cortex for memories of shapes)

• What affects the vividness and length of memories?– Emotional State– Repetition– Association (mnemonic devices)

Protection of the Brain• Meninges (Physical protection)

• Cerebrospinal Fluid (Physical Protection)

• Blood-Brain Barrier (Chemical Protection and Immune Function)

Meninges• Sheets of fibrous

connective tissue that surrounds the brain– Dura Mater

• Continues inferiorly as the spinal dura mater

– Arachnoid membrane– Pia mater

Dura Mater

Cerebrospinal Fluid

• Fills the spaces in and around the brain and spinal cord– Ventricles– Meninges

• Absorbs shock, provides buoyancy and delivers materials (electrolytes, etc.) to the brain

Spinal Tap• CSF may need to be sampled to check for

infection/injury– No blood/bacteria should be isolated from CSF in

healthy individuals

Blood-Brain Barrier

• Brain needs to be protected from – Pathogens– Wild swings in chemistry

• Capillaries serving the brain are only permeable to the smallest molecules essential for brain function– Tight junctions in blood vessel epithelia– Astrocytes – limit what comes in and out of brain tissue

Always a good thing?

Concussion• Generally due to a violent jarring or twisting of

the brain inside the cranium

Progressive Brain Diseases

• What types of diseases are responsible for slow, progressive loss of mental function?

• Name of disease• Symptoms• Mode of pathology• Prognosis• Treatment

Spinal Cord - Anatomy

• Enclosed by the neural arches of the vertebrae

• Extends from the base of the skull to the 1st-2nd lumbar vertebrae

Spinal Cord - Function

• Provides afferent and efferent nerve pathways to and from the brain and peripheral nerves

• Major reflex center

Spinal Cord – Protection

• Resides within the spinal canal (vertebrae)

• Also surrounded by meninges– Spinal Dura Mater– Arachnoid Membrane– Pia Mater

• CSF between arachnoid membrane and pia mater

Spinal Meninges

Epidurals

• Anesthetic is placed in epidural space using a fine needle (catheter)

• Often used during labor, surgery or diagnostic procedures

Spinal Cord Terminus

• Spinal cord ends at the conus medullaris at 1st-2nd Lumbar vertebra

• Filum terminale anchors the spinal cord to the coccyx

• Nerve roots for lumbar and sacral region extend through the vertebral canal and exit through their respective vertebrae

Cauda Equina

Spinal Cord Cross-Sectional Anatomy