Biology 30 AP - Nervous System & Senses

Central nervous system (CNS)

the body’s coordinating center for mechanical and chemical actions

brain & spinal cord

Outer region of CNS

white matter

protected by oligodendrocytes which have a myelin sheath

Inner region of CNS

does NOT have a myelin sheath

Functions of CNS

relays nerve impulses to and from the brain

uses sensory and motor neutrons

controls spinal reflexes

Peripheral nervous system (PNS)

all parts of the nervous system excluding brain and spinal cord

relay information between the CNS and other parts of the body

Glial (neuroglial) cell

non-conducting cells

important for structural support and metabolism of nerve cells

Neurons

functional units of nervous system

conducts nerve impulses

Dendrites

receive information from either environment or other neurons

projection of cytoplasm that carries impulses towards cell body

Axon

extension of cytoplasm that carries the nerve impulses away from the cell body

Myelin sheath

white coat of fatty protein

acts as insulation for the neurons

Schwann cell

special type of glial cell that produces myelin sheath

Nodes of Ranvier

regularly occurring gaps between section of myelin sheath along axon

Neurilemma

delicate membrane

surrounds axon of SOME nerve cells

promotes the regeneration of damaged axons

not all nerve cells that have a myelin sheath have a neurilemma (CNS lacks neurilemma)

Types of neurons

sensory (afferent)

interneuron

motor (efferent)

Sensory (afferent)

relay information or stimuli received by sensory receptors about the internal/external environment to the CNS for processing

Interneurons

links neurons to other neurons

found only in brain and spinal cord

integrate and interpret the sensory information and connect to outgoing motor neurons

Motor (efferent)

relay information to the effectors (cell/organ that responds)

effectors: muscles, organs, glands

Reflex arc

simplest nerve pathway

involuntary/unconscious

do not require coordination by the brain

stimulus → receptor → sensory neuron → interneuron → motor neuron → effector → response

Steps of the reflex arc

1. The stimulus is detected by receptors in the skin

2. Receptors initiate nerve impulses in the sensory neurons leading from them to the spinal cord

3. Impulses enter the spinal cord and initiate impulses in one or more association/interneurons

4. Association/interneurons initiate impulses in the appropriate motor neurons

5. When these impulses reach the junction between the motor neurons and the muscles, the muscles are stimulated to contract and the hand is withdrawn