Nervous System
Connective Tissue Coverings
Cranial Nerves
Spinal Nerves
Neurotransmitters:chemical messengers in a synapse, that convey an electrical impulse from a neuron to another cell
Autonomic Nervous System
Major functions of Brain (4 main parts)
Major functions of spinal cord
Divisions and Subdivisions
Peripheral Nervous System
Central Nervous System
Brain and Spinal Cord
decision-making
cranial and spinal nerves that connect the CNS to the rest of body
Contains sensory(afferent) and motor(efferent) divisions
Motor functions: Somatic Nervous System: controls voluntary skeletal muscles; Autonomic Nervous System: controls involuntary effectors(smooth and cardiac muscles and glands)
General Functions
Sensory Function
Integrative Function
Motor Function
Provided by sensory effectors detecting internal and external changes
Coordination of sensory information in the CNS(decision-making)
Information travels from receptors to sensory neurons, which transport information into the CNS
Nerve impulses(CNS) are conducted along motor neurons to effectors
Effectors are muscles or glands that respond to decisions made in the CNS
Tissues
Neurons
Neuroglia
Astrocytes lie between blood vessels and neurons; functions: structural support; formation of blood-brain barrier, protecting brain tissue from chemical fluctuation and prevents entry of many substances
Peripheral nervous system: Schwann Cells: the myelin-producing neuroglia of the PNS; Satellite cells: provide protective coating around cell bodies of neurons in the PNS
Action Potential
occurs when it the charge reaches -55mV
when its reached, cells respond by returning to resting potential -70mV by process of repolarization
At the end of repolarization a slight overshoot called hyperpolarization occurs in which potential dips below -70mV
repolarization is accomplished by outward flow of potassium ions through potassium channels
Finally the Na+/K+ pumps moves Na+ ions back out of cell, and K+ back into cell
Sensory(afferent) neurons: conduct impulses from peripheral receptors to the CNS; usually unipolar, although some are bipolar
Interneurons(association or internuncial neurons):multipolar neurons lying within the CNS that form links between other neurons
Motor(efferent) neurons: multipolar neurons that conduct impulses from the CNS to peripheral effectors(muscle& glands)
12 pairs arise from the underside of brain
most are mixed containing sensory & motor nerve fibers some are sensory others are primarily motor
the first pair arises from the cerebrum and the second pair from the thalamus, but most arise from the brainstem
31 pairs, all except the first pair are mixed nerves
each arises from two roots: a sensory dorsal root, and a motor ventral root
Each dorsal root and doral root unite to form a spinal nerve which extends out of the vertebral canal through the intervertebral foramen
Reflex Behavior
Controls visceral motor functions of smooth muscle cardiac muscle and glands
Helps maintain homeostasis, responds to emotional stress, and prepares the body for strenuous activity
Controls heart rate, blood, pressure, breathing rate, body temperature
Transmit impulses to & form the brain, & to house spinal reflexes
Ascending tracts carry sensory information to brain;descending tracts carry motor information from brain to muscle or glands
spinal reflexes controlled by reflex arcs that pass through the spinal cord
The Patellar Reflex(upright posture)
Withdrawal Reflex
Striking the patellar ligament stretches to the quadriceps muscle, and tendon, stimulating stretch receptors
Sensory neurons transmit nerve impulses to the spinal cord, where the synapse with motor neurons, and issue a motor command
Motor neurons transmit the impulses to the quadriceps muscle which contracts in response;this extends the knee
occurs in response to touching something painful, such as stepping on a tack
involves sensory neurons, interneurons, and motor neurons
largest, most complex portion of the nervous system
Structure is reversed from that of spinal cord; gray matter outside & white matter inside
Cerebrum: largest portion; associated with higher mental functions of the brain: and sensory & motor functions, and sensory & motor functions
Diecephalon: processes sensory input and controls many homeostatic processes
Cerebellum: coordinates muscular activity
Brainstem: coordinates and regulates visceral activities, and connects different parts of the nervous system
Epineurium: outer covering of nerve
Perineurium: covering around fascicles(bundles)of nerve fibers
Endoneurium: covering around individual nerve fiber(axons).
Impulse Conduction
Refractory period: limits frequency of action potentials; ensures the impulse is only transmitted in one direction-down the axon
Continuous Conduction: occurs in unmyelinated axons; conduct impulses sequentially over the entire length of their membrane
Saltatory Conduction: occurs in myelinated axons; the mylein sheath insulates axons from ion movement across the cell membrane
Divisions
Sympathetic:Short preganglionic fibers in the sympathetic division arise from neurons in the gray matter in the thoracic and lumbar regions of the spinal cord
Parasympathetic: long preganglionic fibers in the parasympathetic division arise from the brainstem and sacral region of the spinal cord