The Nervous System

Divisions of the Nervous System Central 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 Cells CNSastrocyteoligodendrocytemicroglialependymal PNSsatelliteSchwannMyelin Sheath – fatty covering of axons 80:20 Phospholipid : 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 filum terminale The pia is on the surface of the CNS and forms the filum terminale which anchors the spinal cord onto the sacrum/coccyx

The Spinal Cord Extends from foramen magnum to the 2 nd or 3 rd lumbar vertebrae medulla oblongata The uppermost portion is called the medulla oblongata conus medullaris cauda equina The lowermost portion is called the conus medullaris and gives rise to the cauda 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

Dermatomes Each 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