Unit 3 Compendium 1- Nervous Function

Table of Contents
I. Nervous System
A. Overview of the Nervous System
B.The Central Nervous System
C. The Limbic System and Higher Mental Functions
D. The Peripheral Nervous System
E. Drug Abuse
II. Senses
A. Sensory Receptors and Sensations
B. Proprioceptors and Cutaneous Receptors
C. Senses of Taste and Smell
D. Sense of Vision
E. Sense of Hearing
F. Sense of Equilibrium



I. Nervous System
A. Overview of the Nervous System
1. The Nervous System is divided into two parts:
a. Central Nervous System (CNS)- Brain and Spinal Cord
b. Peripheral Nervous System (PNS)- Nerves
2. The three main functions: recieves sensory input, performs integration, and generates motor output.
3. Nervous tissue contains two types of cells:
a. Neurons- transmit nerve impulses
b. Neuroglia- nourish and support neurons
4. A neuron is composed of a cell body, dendrites, and an axon. There are three types of neurons:
a. Sensory- take nerve impulses from sensory receptors to the CNS.
b. Interneurons- recieve input from sensory neurons and other interneurons within the CNS
c. Motor- take nerve impulses from the CNS to effectors (muscles or glands)
5. Myelin Sheath- covering formed by a type of neuroglia called Schwann Cells, which contain myelin (a lipid substance) in their plasma membrane.
6. Nerve Impulses convey information within the nervous system
a. Resting Potential- more Na+ outside the axon and more K+ inside the axon. The axon doesn't conduct an impulse.
b. Action Potential- a change in polarity across the axonal membrane as a nerve impulse occurs: When Na+ gates open,Na+ moves to the inside of the axon, and a depolarization occurs. When K+ gates open and K+ moves to the outside of the axon, a repolarization occurs.
7. Synapse- the junction between neurons consisting of the presynaptic (axon) membrane, the synaptic cleft, and the postsynaptic (usually dendrite) membrane.
a. When a neurotransmitter is released into a synaptic cleft, transmission of a nerve impulse occurs.
b. Binding of the neurotransmitter to receptors in the recieving membrane causes excitation or inhibition.
c. Integration is the summing of excitatory and inhibitory signals.
B. The Central Nervous System (CNS) recieves and integrates sensory input and formulates motor output. The CNS consists of the spinal cord and the brain.
1. Spinal Cord- the nerve cord that is continuous with the base of the brain plus the vertibral column that protects the nerve cord.
a. Gray matter of the spinal cord contains neuron cell bodies.
b. White matter consists of myelinated axons that occur in tracts.
c. Conduction to and from the brain; carries out reflex actions.
2. The Brain- enlarged superior portion of the CNS located in the cranial cavity of the skull.
a. Cerebrum- has two cerebral hemispheres connected by the corpus callosum.
a1. Sensation, reasoning, learning and memory, and language and speech take place in the cerebrum.
a2. The cerebral cortex covers the cerebrum. The cerebral cortex of each cerebral hemisphere has four lobes: frontal, parietal, occipital, and temporal.
a3. The primary motor area in the frontal lobe sends out motor commands to lower brain centers, which pass them on to motor neurons.
a4. The primary somatosensory area in the parietal lobe recieves sensory information from the lower brain centers in communication with sensory neurons.
a5. Association areas are located in all of the lobes.
b. The Diencephalon- the hypothalamus controls homeostasis; the thalamus sends sensory input on to the cerebrum.
c. The Cerebellum- coordinates skeletal muscle contractions.
d. The Brain Stem- the medulla oblongata and the pons have centers for breathing and the heartbeat.
C. The Limbic System and Higher Mental Functions
1. The limbic system lying deep in the brain is involved in determining emotions.
2. The amygdala determines when a situation deserves the emotion of fear.
3. The hippocampus is particularly involved in storing and retrieving memories.
a. Short Term Memory- retention of information for only a few minutes, such as remembering a phone number.
b. Long Term Memory- retention of information that lasts longer than a few minutes.
c. Semantic Memory- capacity of the brain to store and retrieve information with regard to words and numbers.
d. Episodic Memory- capacity of the brain to store and retrieve information with regard to persons and events.
e. Skill Memory- involved in performing motor activities such as riding a bike or playing hockey.
D. The Peripheral Nervous System (PNS)
1. The PNS contains only nerves and ganglia.
2. Cranial Nerves take impulses to and from the brain.
3. Spinal Nerves take impulses to and from the spinal cord.
4. The PNS is divided into the Somatic System and the Autonomic System.
a. Somatic System- serves the skin, skeletal muscles, and tendons.
a1. Some actions are due to reflexes, which are automatic and involuntary.
a2. Other actions are voluntary; originate in the cerebral cortex.
b. Autonomic System- the two divisions in this system are the Sympathetic division (responses that occur during thimes of stress) and the Parasympathetic division (responses that occur during times of relaxation).
b1. Actions in these divisions are involuntary and automatic.
b2. These divisions innervate internal organs.
b3. Two neurons and one ganglion are utilized for each impulse.
E. Drug Abuse
1. Neurological drugs either promote or prevent the action of a particular neurotransmitter.
a. Alcohol, Nicotine, Cocaine, Methamphetamine, Heroin, Marijuana, etc.
2. Dependancy occurs when the body compensates for the presence of neurological drugs.
II. Senses
A. Sensory Receptors and Sensations.
1. There are four types of sensory receptors:
a. Chemoreceptors- sensory receptor that is sensitive to chemical stimuli (taste and smell)
b. Photoreceptors- sensory receptor in the retina that responds to light stimuli
c. Mechanoreceptors- sensory receptor that responds to mechanical stimuli (pressure, sound waves, gravity)
d. Thermoreceptors- sensory receptor that is sensitive to changes in temperature
2. Sensory receptors initiate nerve impulses that are transmitted to the spinal cord and/or brain
3. Sensation occurs when nerve impulses reach the cerebral cortex
4. Perception is an interpretation of sensations
B. Proprioceptors and Cutaneous Receptors
1. Proprioceptors- mechanoreceptors involved in reflex actions; help maintain equilibrium and posture.
2. Cutaneous Receptors- sense touch, pressure, temperature, and pain; found in the skin.
C.Senses of Taste and Smell
1. Taste and smell are due to chemoreceptors that are stimulated by molecules in the environment.
a. Sense of taste- microvilli of taste cells have receptor proteins for molecules that cause the brain to distinguish sweet, sour, salty, and bitter tastes.
b. Sense of smell- the cilia of the olfactory cells have receptor proteins for molecules that cause the brain to distinguish odors.
D. Sense of Vision
1. Vision depends on the eye, the optic nerves, and the visual areas of the cerebral cortex.
2. Anatomy and Physiology of the Eye
a. The sclera (outer layer) protects and supports the eyeball
b. The choroid (middle, pigment layer) absorbs stray light rays
c. The retina (inner layer) contains the rod cells (sensory receptors for dim light) and cone cells (sensory receptors for bright light and color).
d. Function of the Lens- the lens, assisted by the cornea and the humor, brings the light rays to focus on the retina. To see an object up close, visual accommodation occurs as the lens rounds up.
e. Visual Pathway to the Brain- the visual pathway begins when light strikes photoreceptors (rod cells and cone cells) in the retina. The optic nerves carry nerve impulses from the eyes to the optic chiasma, then pass through the thalamus before reaching the primary vision area in the optical lobe of the brain.
3. Abnormalities of the Eye
a. Color Blindness
b. Misshapen eyeballs- cause of nearsightedness, farsightedness, and astigmatism.
E. Sense of Hearing
1. Hearing depends on the ear, the cochlear nerve, and the auditory areas of the cerebral cortex.
2. Anatomy and Physiology of the Ear
a. In the outer ear, the pinna and the auditory canal direct sound waves to the middle ear.
b. In the middle ear, the tympanic membrane and the ossicles (malleus, incus, and stapes) amplify sound waves.
c. In the inner ear, the semicircular canals detect rotational equilibrium; the utricle and saccule detect gravitational equilibrium; and the cochlea houses the spiral organ, which contains mechanorecepting for hearing.
d. Auditory Pathway to the Brain- begins when the outer ear recieves and the middle ear amplifies sound waves that then strike the oval window membrane.
e. The mechanoreceptors for hearing are hair cells on the basilar membrane of the spiral organ.
f. Nerve impulses begin in the cochlear nerve and are carried to the primary auditory area in the temporal lobe of the cerebral cortex.
F. Sense of Equilibrium
1. The ear also contains mechanoreceptors for equilibrium
a. Rotational Equilibrium Pathway- mechanoreceptors (hair cells) in the semicircular canals detect rotational and/or angular movement of the head.
b. Gravitational Equilibrium Pathway- mechanoreceptors (hair cells) in the utricle and saccule detect head movement in the vertical or horizontal planes.