NERVOUS SYSTEM Two major divisions

1. Central Nervous System (CNS)2. Peripheral Nervous System (PNS)

Three specific functions1. Receives sensory input2. Performs integration of all input3. Generates motor output

Nervous Tissue Contains two types of cells

1. Neuroglial cells(make up more than half the brain)

2. Neurons Neuroglial cell function

1. Structural and protective2. Support and nourish neurons3. Insulation and development guide (myelin sheath)

Nervous Tissue (cont’) Neurons

1. Three types of neurons a. Sensory neurons – transmit nerve

impulses from stimulus to the CNS b. Interneurons – in central nervous

system c. Motor neurons – instructions away from

to muscles or glands. 2. Parts of a neuron: dendrites, cell body-

nucleus, axon, myelin sheath & nodes of Ranvier

Myelin Sheath In the PNS, the neuroglial cells responsible

for myelination are called Schwann cells In the CNS, Schwann cells are absent,

therefore myelin is provided by oligodendrocytes

Speeds signal conduction Made of lipids and phospholipids Guides nerve regeneration Attacked by immune system in multiple

sclerosis

The Nerve Impulse All cells have a membrane potential or

voltage (electrical charge) across their plasma membrane

At rest, when no nerve impulse is being received, the potential is about - 65mV1. Potential due to difference in Na+

and K+ concentration across the axon membrane2. K+ able to cross axon membrane, Na+not

The Nerve Impulse cont’3. Build up of neg. charge results inside

axon and more pos. charge outside, hence membrane potential = -65mv

When the axon receives an impulse, the membrane potential changes 1. When the membrane potential reaches – 40Mv (threshold level), Na+ channels open 2. Influx of Na+ causes depolarization of the membrane to occur3. When the membrane potential reaches +40mV, K+ channels open – repolarization occurs 4. Inside of axon reverts to pre-dominant neg chg.

The Nerve Impulse cont’ When an impulse has passed a

section of an axon, a refractory period begins (period following an action potential when a neuron can’t conduct another impulse) as the sodium channels are unable to open.

This keeps the impulse running down the axon in the same direction

The Synapse Synapses separate one neuron form another Neurons physically do not touch one another A synapse is a gap that separates neurons Neurotransmitters released from the terminal

bulb enter into the synapse and move across the space (called the synaptic cleft) by diffusion

Neurotransmitters leave the presynaptic neuron and diffuse toward the postsynaptic neuron, where they settle on receptors and initiate a reaction

Neurotransmitters carry the message across the synapse

Neurotransmitters are chemicals that carry an impulse across the synaptic cleft

The Central Nervous System The brain has four main parts

Brain stem + midbrain Diencephalon Cerebellum Cerebrum The entire brain is involved in the

integration of sensory input and motor responses.

Each section has a slightly different role

Brain cont’ Brain stem – medulla oblongata and pons

and midbrain Regulates heart rate, breathing and blood

pressure Portion of the brain (anatomically and

physiologically) closest to the spinal cord Cerebellum

Maintains muscle tone, posture and balance, and fine-tuning conscious and unconscious movement

Portion of the brain posterior to the brain stem

Brain cont’ Diencephalon

Functions mainly as a relay center for sensory information from the body and motor responses from the cerebrum (including centers for visual and auditory startle reflexes)

The thalamus and hypothalamus are located in the diencephalon

Brain cont’ Cerebrum

Largest portion of the brain, integrates information and generates appropriate responses

The center of the brain responsible for learning, remembering and planning activities

Spinal cord Extends from the brain into the

vertebral column It is the main route of

communication between the brain and the body

The spinal cord connects to almost every organ

Protection and Support Meninges:3 layers around brain and spinal

cord Three connective tissue membranes Inflammation is meningitis

Cerebrospinal fluid Absorbs shocks and nourishes neurons There are four ventricles (cavities) in the brain

filled with CSF – circulates around spinal cord Reabsorbed in brain; if not working,

hydrocephaly

Protection and Support The axial skeleton provides bony

protection for the CNS What separates the CNS from the

axial skeleton? Meninges and Cerebrospinal fluid

Damage to neurons in the CNS is generally not repaired The oligodendrocyte retreats and

leaves no tube (myelin sheath) or pathway to aid in axonal regrowth

In the PNS, neurons can recover from some damage because the Schwann cell axonal tube remains

CNS - review The brain (skull) and spinal cord

(vertebral column) are encased in the skeleton and are covered by meninges

It is the main integration center of the body

Sensory information enters the CNS, where it is analyzed and an appropriateresponse is generated

Motor information leaves the CNS and brings about the body’s response.

Peripheral Nervous System The neurons of the PNS are arranged

in bundles called nerves Nerves can be motor, sensory or

mixed depending on the neurons they contain

Information traveling to and from the CNS must go through the PNS

The PNS picks this information by: Special senses receptors: enable us to

see, hear, taste, and smell General sensory receptors: found in

our skin and inform us about temperature, light touch, pressure, and pain

Visceral receptors: monitor proprioception (help control movement and awareness of limb position) and organ functioning

The Autonomic Nervous System

This division of the PNS governs our body’s responses to subtle changes in homeostasis

There are 2 subdivisions Sympathetic – includes the nerves that

control the body when it is actively moving and burning energy – also called the “Fight, Flight, Fright” system.

Parasympathetic is responsible for digestion, energy storage, and relaxation. “Rest and Digest” system.