Nervous System Anatomy and Physiology

The master controlling and communicating system of the body Functions: –Sensory input – monitoring stimuli occurring inside and outside the body –Integration – interpretation of sensory input –Motor output – response to stimuli by activating effector organs What are the major functions of the nervous system?

How is the nervous system organized? Central nervous system (CNS) –Brain and spinal cord –Integration and command center Peripheral nervous system (PNS) –Paired spinal and cranial nerves –Carries messages to and from the spinal cord and brain

Sensory (afferent) division –Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain –Visceral afferent fibers – transmit impulses from visceral organs to the brain Motor (efferent) division –Transmits impulses from the CNS to effector organs What are the divisions of the peripheral nervous system?

Somatic nervous system –Conscious control of skeletal muscles Autonomic nervous system (ANS) –Regulate smooth muscle, cardiac muscle, and glands –Divisions – sympathetic and parasympathetic What are the parts of the motor division?

What are the functions of the sympathetic and parasympathetic divisions? Parasympathetic- “resting and digesting system” Most active in nonstressful situations Keeps energy use low and maintains vital housekeeping activities running. Sympathetic division- “fight or flight” division Exercise, excitement, emergency, and embarrassment division Prepares the body for action

What types of supporting cells make up central nervous tissue? Known as neuroglia or glial cells 1. Astrocytes-star shaped cells that connect neurons together and to their blood supply. 2. Microglia- function as phagocytes by engulfing foreign invaders. 3. Ependymal- (epithelial-like) provide a barrier between brain and spinal fluid. 4. Oligodendrocytes- connect thick neuronal fibers and produce an important insulating material called the myelin sheath.

What are neurons? Conduct messages in the form of nerve impulses They number in the billions (much higher in anatomy teachers) Have extreme longevity Most cannot divide (hippocampus is a rare exception; it is involved in memory). Have a high metabolic rate; require mucho oxygen and glucose 3 basic regions: dendrites, cell body, and axons Impulses travel from dendrites to cell body to axons

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How is a nerve impulse transmitted across a neuron? The sodium-potassium pump creates a resting potential across the membrane of a neuron.sodium-potassium pump resting potential When a threshold stimulus is applied to the neuron, an action potential travels down the neuron. (action potential=nerve impulse)action potential The nerve impulse will jump from the axon to the dendrite of another neuron across a synapse by the use of neurotransmitters

What is the all-or-none phenomenon? An action potential either happens completely or not at all. Many sub-threshold stimuli can cause an action potential. Neurons can have different thresholds (pain) It is similar to the flash point of a burning twig. As a match is placed under a twig, the twig must get hot enough to produce a flame on the twig.

What is saltatory conduction? Myelin sheath found on the axon insulates and doesn’t allow the depolarization of the membrane. The action potential must jump from one node of Ranvier to the next. This makes the action potential move faster down the axon. Some can reach speeds of 100 m/s. Unmyelinated neurons propagate slow action potentials that must move from one site to the next. This is called continuous conduction.

Saltatory conduction

What is a synapse? Synapses are gaps between neurons Synapses Exists between the axon of one neuron and the dendrite of another. Neurons can have a large number connecting to numerous other neurons. (This accounts for the complexity of the nervous system) When an action potential reaches the end of an axon, neurotransmitters are stimulated to flood the gap and bond to ion channels on the post synaptic neuron. This causes an action potential to be produced.

Vesicles with neurotransmitters Synapse

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What are neurotransmitters? Molecules that bridge the synapse Over 50 different types have been discovered Some can be excitatory or inhibitory See page for types

What are reflexes? Rapid, automatic responses to stimuli, in which a particular stimulus always causes the same motor response. Produces the simplest behaviors. Ex. Removing hand from a hot object. Occur over neural pathways called reflex arcs. 5 basic components: receptor, sensory neuron, integration center, motor neuron, and effector.

What are the major parts of the brain? Cerebral hemispheres, diencephalon, Brain stem, and cerebellum Cerebrum and cerebellum have a gray matter nuclei surrounded by white matter and a gray matter cortex. Gray matter- unmyelinated neurons White matter- myelinated neurons

What are the functions of the cerebral cortex? Interprets sensory impulses (including auditory,visual, and olfactory), controls voluntary and skilled skeletal muscle, functions in intellectual and emotional processing. Shows lateralization of function –Most people the left hemisphere is dominant and is specialized for language and mathematical skills –The right hemisphere is more concerned with visual- spatial skills and creative endeavors. –Right hemisphere controls the left side of the body (motor control) and vice versa.

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What are the functions of the diencephalon? Consists of the thalamus, hypothalamus and epithalamus and encloses the third ventricle. Thalamus- Relay station for sensory and motor impulses to and from the cerebrum. Functions in memory. Hypothalamus- Regulates hormonal output of the pituitary gland, regulates body temp., food intake, water balance, thirst, and biological rhythms and drives. (limbic system) Limbic System- functional system involving cerebral structures and the diencephalon that mediates emotional responses and is also involved in memory.

What are the parts and functions of the brain stem? Medulla oblongata- respiratory rhythm, heart rate, and blood pressure Pons- regulation of respiration Midbrain- visual and auditory reflex centers and fear response

What is the function of the cerebellum? Cerebellum processes and interprets impulses from the motor cortex making movements smooth and well timed. (coordination)

What protects the brain? The brain is protected by bone, meninges, cerebrospinal fluid, and the blood-brain barrier. Meninges have 3 layers: –Dura mater- tough layer of fibrous connective tissue –Arachnoid mater- filled with large blood vessels and CSF –Pia mater- delicate connective tissue with capillaries Blood-brain barrier- keep blood products separate from neurons. Formed from tight capillary walls and ependymal cells that form a tight membrane around capillaries. CSF- liquid cushion produced by the choroid plexus and fills the cranial cavity.

Blood-brain barrier

What is the spinal cord? Two-way impulse conduction pathway and a reflex center. Lies within the vertebral column Protected by meninges and CSF 31 pairs of spinal nerve roots extend from the cord.