Structure and Function of the Nervous System

Peripheral Nervous System: Cranial nerves (12 pairs) Spinal nerves (31 pairs) Afferent (ascending) – sensory Efferent (descending) – motor Central Nervous System: Brain Spinal cord

Central Nervous System

Peripheral Nervous System Somatic Nervous Autonomic Nervous System System Operates with conscious control              Usually without conscious control Controls skeletal muscle Regulates body’s internal environment Releases Acetylcholine at synapses               Releases acetylcholine or norepinephrine at                                                                            synapses

Autonomic Nervous System Sympathetic Parasympathetic Nervous System Nervous System Originates in the thoracic Originates in the brain stem and lumbar segments         (cranial nerves) and sacral of the spinal cord : segments of the spinal Thoracolumbar system cord: Craniosacral system

Sympathetic Parasympathetic Nervous System Nervous System Effect is wide spread            Effect is local "Fight-or-Flight" - Bear           "Feed and Breed” - Book emergency, excitement, exercise,            salivation, lacrimation, urination,   embarrassment defecation                                                                                       Postganglionic fibers Postganglionic fibers release norepinephrine     release Ach Preganglionic fibers of both release ACh

Cells of the Nervous System Neurons – the primary cell of the nervous system Supporting cells – Neuroglial cells

Neurons Each neuron is adapted for a specialized function. Detect environmental changes Process information Initiate body responses Fuel source is mostly glucose

Saltatory conduction

Neuroglia – “Nerve glue” Schwann cells form the myelin sheathes of axons in the peripheral nervous system. Astrocytes Oligodendrocytes Microglia Ependymal cells are found in the CNS

Generation of nerve impulses Action potentials are generated when stimulus is greater than threshold. Action potential is an all-or-none response Axon has a resting potential Opening of voltage gated channels propagates current down axon At end of axon, neurotransmitters released from synaptic knobs into synaptic cleft

Neurons interact with other neurons Synapse – region between two neurons Presynaptic → Postsynaptic Neurotransmitters: Excitatory – Excitatory postsynaptic potentials (depolarize) Inhibitory – Inhibitory postsynaptic potentials (hyperpolarize –more difficult to reach threshold)

Neurotransmitters At least 30 known Acetylcholine Amino acids – GABA Biogenic amines – catecholamines – norepinephrine, epinephrine, dopamine Also serotonin and histamine Neuropeptides – opiates such as enkephalins and endorphins Gases – Nitric oxide (NO)- vasodilation

Brain

Divisions of Brain Forebrain - cerebral hemispheres, thalamus and hypothalamus Midbrain - corpora quadrigemina and cerebral peduncles Hindbrain - cerebellum, pons, medulla oblongata Reticular formation Reticular activating system

Gyri - convolutions Sulci - grooves Gray matter – nerve cell bodies and dendrites (unmyelinated) White matter – myelinated axons

Spinal cord Lies in vertebral canal protected by vertebral column Connects brain and body Somatic and autonomic reflexes Begins at medulla oblongata and ends at conus medullaris at L1 or L2

Protective Structures Cranium Meninges: Dura Mater – “Tough mother” Periosteum and meningeal layer Falx cerebri, Falx cerebelli, and Tentorium cerebelli Arachnoid – “Spider web-like” Subarachnoid space – CSF flows Pia mater – “Gentle mother”

Blood-Brain Barrier Capillaries have tight junctions Aided by astrocytes Selectively permeable Important when we want to get antibiotics or other chemotherapeutic agents into the brain.