The Nervous System

Divisions of the Nervous SystemCentral Nervous System [CNS] = Spinal Cord

Brain

Peripheral Nervous System [PNS]= Spinal Nerves [31 pair]

Autonomic Nervous System [ANS]

Sympathetic Division

Parasympathetic Division

Cranial Nerves [12 pair]

Cells of the Nervous System

• Neurons are the functional cell of the system

• Have 3 basic parts to them

Body [soma]

Axon

Dendrites

• Neuroglial [glial] are the supporting cells of the system. They are smaller and more plentiful than neurons. In some areas, there are 10x more neuroglial cells than neurons.

Neuroglial CellsCNS astrocyte oligodendrocyte microglial ependymal

PNS satellite Schwann Myelin Sheath –

fatty covering of axons

80:20Phospholipid

: protein

astrocyte

microglial

oligodendrocyte

Nerve Conduction

• Action Potential – generated by change in membrane’s permeability which causes an exchange of ions – caused by impulse

Resting state of cell – polarized

receiving stimulus – depolarized

returning to resting state - repolarized

At rest, inner environment has a higher concentration of K, the outer environment has a high Na concentration. The neuron’s cell membrane has active Na/K gates. When an impulse comes in contact with the membrane, it turns off the gate.[polarized]

Na rushes in, K leaves and the electrical impulse passes through the cell body. [wave of depolarization]

After the electrical impulse leaves, the gates are turned back on, and Na is pumped out - K reenters the cell

3 Na pumped out for every 2 K pumped in [repolarization]

The Synapse

Gap between two cells

Information can ‘jump’ gap via a chemical [neurotransmitter] or electrical signal.

Electrical synapses cross gap junctions, such as in cardiac and smooth muscle.

Neurotransmitters are used in nervous system synapses. They are released from the axon. Bouton / knobs / presynaptic terminal

Neuromodulators – can influence an action potential

Meninges

• The CNS is covered in a protective membrane

• Dura mater

• Arachnoid mater– Subarachnoid space – Cerebral

Spinal Fluid

• Pia mater

The pia is on the surface of the CNS and forms the filum terminalefilum terminale which anchors the spinal cord onto the sacrum/coccyx

The Spinal Cord

Extends from foramen magnum to the 2nd or 3rd lumbar vertebrae

The uppermost portion is called the medulla oblongatamedulla oblongata

The lowermost portion is called the conus medullarisconus medullaris and gives rise to the cauda equinacauda equina

Spinal Cord Anatomy

• White matter – myelinated axons

• Gray matter – cell bodies

• Anterior – median fissure

• Posterior – median sulcus

• Central canal

• Commissure = connecting nerve fibers from one side to other

• Posterior horn- receives sensory / afferent input

• Anterior horn – transmits motor/efferent response

• Columns – pathways / nerve tracts

Cross Section of Spinal Cord

DermatomesEach spinal nerve, except C1, has a specific cutaneous sensory distribution

Letters and numbers indicate the spinal nerves that innervate a given region

Reflexes

• Protective mechanism• Automatic response to

a stimulus that occurs without conscious input

• Reflex vs reaction

The Brain

The brain can be divided into 4 regions

• Brain Stem– medulla oblongata

– pons

– midbrain

• Cerebellum• Diencephalon

- thalamus

- hypothalamus

- pituitary/pineal glands

•Cerebrum

-lobes -> frontal, occipital, temporal, parietal, prefrontal

-corpus callosum -> main commissure

-ventricles - spaces where CSF is produced/flows