Ch. 7 Notes
The Nervous System
Introduction
 The nervous system is the master controlling and communication system of the body
 Communicates through electrical impulses
 Every thought, action, and emotion reflects its activity
 Functions
1. Monitor changes (sensory input)
2. Process and interpret sensory input (integration)
3. Effects a response (motor output)
Structural Classification
 Central Nervous System (CNS) – brain and spinal cord
 Occupies the dorsal body cavity
 Acts as the command center of the nervous system
 Peripheral Nervous System (PNS) – nerves that extend from brain and spinal cord
 Consists mainly of the nerves that extend from the brain and spinal cord
 Spinal Nerves – carry impulses to and from the spinal cord
 Cranial Nerves – carry impulses to and from the brain
Functional Classification
 Afferent (sensory) Division - nerve fibers that carry impulses to the CNS
 Keeps the CNS constantly informed on events inside and outside the body
 Efferent (motor) Division - nerve fibers that carry impulses from the CNS to the effector organs
 These impulses activate or bring about a motor response
 Two Motor Subdivisions
 Somatic Nervous System - allows us to consciously or voluntarily control our muscles
 Autonomic Nervous System – regulates events that are automatic or involuntary
 Sympathetic- mobilizes the body during extreme situations
 Parasympathetic- allows us to unwind and conserve energy
Nervous Tissue
 Supporting Cells (neuroglia) - cells that support, insulate, and protect delicate neurons
4 types
 Astrocytes - (star shaped) protect neurons from harmful substances in the blood
 Microglia - dispose of debris and foreign substances (ex. Dead brain cells)
 Ependymal cells - helps circulate cerebrospinal fluid and create a cushion
 Line cavities of the brain and spinal cord
 Oligodendrocytes - insulated covering of nerve cells called myelin sheaths
 Neurons (nerve cells) - transmit messages called a nerve impulse from one part of the body to
another
 Neurons differ structurally but have many common features
 (Ex. They all possess a cell body and one or more processes extending from the
cell body)
 Neurons communicate with each other through tiny gaps called synaptic clefts
(Synapses).
Neurons Anatomy
 Cell Body (perikaryon) - the metabolic center of the neuron
 Contains the usual organelles
 Contains neuroplasm which is the cytoplasm of the neuron
 Nissl Substance (rough ER) – produce proteins
 Neurofibrils – intermediate filaments that are important in maintaining cell shape
 abundant in the cell body
 Processes – arm like extension of the cell body that sends and receive electrical signals
 Can be 3 to 4 feet (Ex. Lumbar – Big toe)
 Two Types:
 Dendrites – convey incoming messages (electrical signals) – afferent process
 Axons – generate nerve impulses and send them away from the cell body - efferent
process
 Each neuron can have hundreds of dendrites but only 1 axon
 Axon hillock – conelike region where axon meets cell body
 Axon terminals – branches at the end of the axon
 Contain neurotransmitters
 Each axon terminal is separated from the next neuron by a tiny gap called the synaptic
cleft (synapse)
 Schwann cells are supporting cells that wrap themselves around the axon and form the
myelin sheath encloses the axon
The Central Nervous System
 Consists of the Brain and Spinal Cord
 They act as a control center for all activities
 The Brain is divided into four major regions
 Cerebral hemispheres
 Diencephalon
 Brain stem
 Cerebellum
 Fun Facts!
 The brain weighs roughly 3 lbs and is about the size of your two fist put together
 The brain gives us consciousness, memory, perception, and the ability to evaluate
situations and feel emotions
Cerebral Hemispheres
 Together called the cerebrum, the most superior part of the brain
 Frontal lobe: Conscience choice, motor movements, speech, language comprehension.
 Temporal lobe: auditory, olfactory, long term memory.
 Parietal lobe: somatic sensory (pain, temp., touch), gustatory,
 Occipital lobe: vision , spatial interpretation
Diencephalon (Interbrain)
 Thalamus: recognizes pleasant and unpleasant senses, sleep, alertness
 Hypothalamus: regulation of temperature, water balance,metabolism, moods,regulates sex
drive and emotional memory (Limbic system)
 Pituitary gland: important in hormone production “Master Hormone Gland”
Brain Stem
 Midbrain: vision and hearing reflexes
 Pons: breathing
 Medulla Oblongata: regulates heart rate, blood pressure, breathing, swallowing, and vomiting
 Reticular Formation: motor control of the visceral organs (abdomen)
 Damage to this area can result in permanent unconsciousness (coma)
Cerebellum
 Large cauliflower projection under the occipital lobe
Functions:
1. Skeletal muscle activity
2. Balance and equilibrium (Coordination)
3. Regulates body position and tension of body parts
The Spinal Cord
 A continuation of the brain stem
 Extends from brain to just below ribs (L1)
 Enclosed in vertebral column
 Creates a two way pathway to and from the brain
Gray Matter
 Butterfly in shape
 Surrounds central the central canal of the spinal cord
 Damage can cause loss of sensation from body area
 Contains motor neurons of the somatic (voluntary) nervous system
White Matter
 Surrounds the gray matter
 Conducts impulses to the brain for sensory (afferent) and motor (efferent)
Peripheral Nervous System
 Consists of nerves and scattered neuronal cell bodies found outside of the Central Nervous
System
 Cranial nerves- 12 pairs of nerves that extend from the brain
 Spinal nerves- 31 pairs of nerves that extend from the spinal cord
Cranial Nerves
 Olfactory nerve - carries impulse for sense of smell
 Optic nerve - carries impulse for vision
 Oculomotor nerve - supplies motor fibers for eye muscles
 Facial nerve - activates muscle for facial expression and impulse for taste
 Vagus nerve - sensory and motor impulses for respiratory, cardiac and digestive activity
 Trochlear – supplies motor fibers for one external eye muscle
 Trigeminal – conducts sensory impulses from the skin of the face and mucosa of the nose and
mouth: activates chewing muscles
 Abducens – supplies motor fibers to the lateral rectus muscle – rolls the eye laterally
 Vestibulocochlear – sensory; transmits impulses for the sense of balance and hearing
 Glossopharyngeal – supplies motor fibers to the pharnyx to promote swallowing and saliva
production
 Accessory – motor fibers that activate sternocleidomastoid and trapezius muscle
 Hypoglossal – motor fibers control tongue movements
Spinal Nerves
 Named from vertebrae from which the extend
 C1-C5 (Cervical)- serves muscles of shoulder and neck
 C5-C8, T1 (Brachial)- serves shoulder and arm muscles
 T2-T12 (Thoracic)- serves muscles between ribs and mid trunk
 L1-L4 (Lumbar)- serves muscles of abdomen, hips and upper leg
 S1-S4- (Sacral)- serves muscles of lower leg and feet
 Sciatic Nerve - largest nerve in the body, serves muscles of the legs