Anatomy & physiology

1. Anatomy & physiology Part 1: The Nervous System

2. Three Functions of the Nervous System: • Sensory Input: • Gathers stimuli (receives information) • Integration: • Processes and interprets information • Motor Output: • Causes a response to muscles or glands http://www.google.com/imgres?

3. Organization of the Nervous System: Structural Classification: Functional Classification: • Central Nervous System (CNS): brain & spinal cord • Peripheral Nervous System (PNS): spinal & cranial nerves • Sensory Division (a.k.a. Afferent): nerves carrying info to the CNS from the body • Motor Division (a.k.a. Efferent): nerves carrying info from the CNS to the muscles or glands • This includes: • Somatic Nervous System: voluntary control (skeletal muscles) • Autonomic Nervous System (ANS): involuntary control (smooth & cardiac). This includes: sympathetic & parasympathetic.

4. Supporting Cells of the Nervous System: 1. Microglial cells:support neurons & carry out phagocytosis 2. Oligodendrocytes: form myelin within the brain; occur in rows along nerve fibers 3. Astrocytes: found between neurons & bv’s; support, regulate [nutrients] & [ions], & form scar tissue following a CNS injury. 4. Ependymal cells: membrane like structure that covers parts of the brain(choroid plexuses) & forms inner linings of brain (ventricles) & spinal cord(central canal).

5. http://www.colorado.edu/kines/Class/IPHY3430-200/image/gila.jpghttp://www.colorado.edu/kines/Class/IPHY3430-200/image/gila.jpg

6. Neurons: Nerve Cells • Neurons vary in size, shape & function • Mature neurons do NOT divide • All neurons have: • A cell body is the main component of a neuron. It contains cytoplasm, a cell membrane, a nucleus, & organelles. • The ER of a cell body is called the chromatophilic substanceor nisslbodies (perform protein synthesis). http://www.google.com/imgres?

7. Neuron Anatomy: • Dendrites and axons are nerve fibers that attach to the cell body (most neurons have these). • Dendrites (usually more than 1 on a cell body) are the communication means of one neuron to the next. They receive messages. These are short branched fibers. • Axonstake impulses away from the cell body. They are usually one fiber with side branches.

8. Large axons have a covering sheath called a myelin sheath (a membrane of lipoprotein). • The myelin sheath is composed of Schwann cells (neuroglial cells). • The gaps between the myelin sheaths are called nodes of Ranvier. • In the CNS, white matter are the fibers that are myelinated while gray matter are the fibers that are unmyelinated.

9. http://www.google.com/imgres?

10. A neuron:

11. Terminology: • Nuclei: clusters of cell bodies in the CNS • Ganglia: small clusters of cell bodies in the PNS (outside the CNS) • Tracts (or nerve tracts): bundles of nerve fibers running through the CNS • Nerves: fibers running through the PNS • White Matter: myelinated fibers • Gray Matter: unmyelinated fibers

12. Types of Neurons: Structural Classification: 1. Bipolar neurons: 2 nerve fibers, one at each end (1 axon & 1 dendrite). Found in the nose, eyes, & ears. 2. Unipolar neurons: 1 nerve fiber from the cell body that has 2 branches (1 branch acts as a dendrite & the other branch acts as an axon). 3. Multipolar neurons: many nerve fibers, 1 axon and many dendrites. Found in the brain & spinal cord. http://www.google.com/imgres?

13. Types of Neurons: Functional Classification: 1. Sensory neurons: carry impulses from peripheral body parts to brain & spinal cord (from PNS to CNS). Most are unipolar, some bipolar. 2. Interneurons: carry impulses between neurons. Multipolar neurons. 3. Motor neurons: carry impulses from the brain & spinal cord to the effectors (muscles & glands outside of the NS) to carry out a response. Multipolar.

14. Nerve Impulses: • An unmyelinated nerve fiber carries an impulse slower than a myelinated nerve fiber. • Nerve impulses range in speed according to their diameter (thicker=faster). Ex: skeletal muscle travels ~120 meters/second • Nerve impulses respond in anall-or-none response. • More stimuli= more impulses (per second), not stronger intensity of impulses.

15. Nerve Impulses: • A synapse is a junction between 2 communicating neurons. The neurons are NOT connected. • A synaptic cleft is the gap between these 2 neurons. • A nerve impulse must jump this gap. • A neurotransmitter is a chemical that enables the impulse to jump the synaptic cleft. http://www.google.com/imgres?

16. Neurotransmitters: • There are 2 types: • Excitatory (increase membrane permeability) -impulse will likely occur • Inhibitory (decrease membrane permeability) -impulse will not likely occur • There are at least 50 known neurotransmitters, including these groups: • Acetylcholine (stimulates skeletal muscles) • Monoamimes (epinephrine, norepinephrine, dopamine, & serotonin) • Several amino acids • Peptides

17. Reflexes: • These are rapid, involuntary responses • A reflex arc is the simplest nerve pathway that contains only a few neurons. • The withdrawal reflex is a protective reflex (pulling your finger away from a hot pot) b/c it limits tissue damage. In addition to this reflex, interneurons also trigger a response to pain. • Somatic reflexes includeskeletal muscles(pulling your hand away from a hot stove). • Autonomic reflexes include smooth and cardiac muscles as well as glands (pupils dilating, mouth ‘watering’) • The knee-jerk reflex is a nerve pathway involving only 2 neurons (1 sensory & 1 motor).

18. Withdrawal Reflex: http://www.mhhe.com/socscience/intro/ibank/ibank/0022.jpg