CHAPTER 7

FUNCTIONS 1. Sensory Input- sensory receptors respond to external and internal stimuli by generating nerve impulses that travel to the brain and spinal cord. 2. Integration- the brain and spinal cord process and interpret sensory input and decide if action is necessary. 3. Motor output- nerve impulses (response) are sent to the effectors, which are muscles & glands.

DIVISIONS of the NERVOUS SYSTEM 1. Central Nervous System (CNS)- includes the brain and spinal cord. Which have a central location (midline) 2. Peripheral Nervous System (PNS)- includes the cranial nerves and spinal nerves, which project off of the spinal cord. Divided into 2 divisions: a. somatic division b. autonomic division

Functional Classification of the Peripheral Nervous System 1. Divided into the sensory and motor divisions 2. Sensory (Afferent) Division- nerve fibers carry information to the central nervous system 3. Motor (Efferent) Division- nerve fibers carry information from the central nervous system; contains 2 subdivisions: a. Somatic nervous system= voluntary b. Autonomic nervous system= involuntary

Organization of the Nervous System

Nervous Tissue 1. Made up of two principal kinds of cells: neurons and neuroglia 2. Neurons- called nerve cells, transmit impulses 3. Neuroglia- support cells which nourish the nerve cells

What are Neurons? 1. Conduct messages in the form of nerve impulses 2. They number in the billions 3. Most cannot divide 4. Have a high metabolic rate, means they require much oxygen and glucose 5. 3 basic regions: dendrites, cell body, and axon 6. Impulses travel from dendrites to cell body to axons

Neuron Anatomy 1. Cell body- contains the nucleus (has a large nucleolus); metabolic center 2. Dendrites (many)- extensions from the cell body; receive impulses 3. Axon (one)- conduct impulses away from the cell body

4. Schwann cells- produce myelin sheaths in a jelly- role like fashion 5. Nodes of Ranvier- gaps in the myelin sheath along the axon

What are Neuroglia? 1. Support cells 2. Four (4) Types of neuroglia: a. Astrocytes-star shaped cells that connect neurons together and to their blood supply; control the chemical environment of the brain. b. Microglia- function as phagocytes by engulfing foreign invaders and disposing of debris c. Ependymal- (epithelial-like) provide a barrier between brain and spinal fluid and the cord and spinal fluid d. Oligodendrocytes- connect thick neuronal fibers and produce an important insulating material called the myelin sheath.

Neurons vs. Neuroglia 1. Neuroglia divide, Neurons do not divide (amitotic) 2. Neuroglia support, insulate, & protect cells. 3. Most brain tumors are “gliomas. 4. Most brain tumors involve the neuroglia cells, not the neurons. 5. Neurons are neurotransmitters.

Nerve Impulse Anatomy 1. Axons end in axonal terminals 2. Axonal terminals contain vesicles with neurotransmitters (chemicals) 3. Axonal terminals are separated from the next neuron by a gap a. Synaptic cleft – gap between adjacent neurons b. Synapse – junction between nerves

How is a nerve impulse transmitted across a neuron? 1. The sodium-potassium pump creates a resting potential across the membrane of a neuron. 2. When a threshold stimulus is applied to the neuron, an action potential travels down the neuron. (action potential=nerve impulse) 3. The nerve impulse will jump from the axon to the dendrite of another neuron across a synapse by the use of neurotransmitters 4. An action potential either happens completely or not at all.