The Nervous SystemChapter 9

General Functions of Nervous SystemMaintain HOMEOSTASIS by:

Receiving, interpreting and integrating sensory information from the environment

Sending signals to muscles and glands so they can respond

Divisions of Nervous System Central Nervous System

(CNS)

Brain Spinal cord

Controls all conscious and unconscious activity

Peripheral Nervous System (PNS)

Cranial nerves Spinal nerves

Connects CNS to the rest of the body

Cranial Nerves

Spinal Nerves

Divisions of PNS Somatic NS

Nerves that connect to skeletal muscles and skin

Controls voluntary/conscious responses

Autonomic NS

Nerves that connect to viscera, heart, smooth muscle, glands

Controls involuntary/subconscious responses

Divisions of Autonomic NS Sympathetic NS

Regulates body’s responses to stress, anger, fear, anxiety…

Controls “fight or flight” mechanisms

Parasympathetic NS

Restores homeostatic conditions after stress, anger, fear…

Controls “rest and digest” mechanisms

Nervous System Structures Functions

Central Brain Spinal cord

Receives/processes sensory info; sends responses to muscles and glands via motor nerves

Peripheral Cranial nervesSpinal nerves

Connects CNS to entire body

Somatic Nerve fibers that connect CNS to skin and skeletal muscles

Controls skeletal muscle; Oversees conscious activity

Autonomic Nerve fibers that connect CNS to viscera, smooth muscle and glands

Controls smooth and cardiac muscle and glands,Oversees involuntary activities; responds to stress

Parasympathetic Nerve fibers from spinal cord to heart, stomach, glands…

Restores body after stress; “rest and digest”

Sympathetic Nerve fibers from spinal cord to heart, stomach, glands…

Preps body for energy expending, stress, emergency, “fight or flight”

Cells of the Nervous System Neurons

-found in CNS and PNS-have unique cells and structure-transmit signals to other neurons

Neuroglial Cells-neuron “helper” cells; not neurons themselves-Found only in CNS

Neurons Include

Dendrites, cell body, and axon Dendrites receive impulses and send them to cell body Axons transmit impulses away from cell body

Neurons in PNS axons are surrounded by SCHWANN CELLS

Schwann cell membranes have MYELIN in them

NEURILEMMA- extra protection around axon

NODES OF RANVIER: narrow gaps in the myelin sheath between Schwann cells

Neurons in CNS Some axons have myelin (MYLELINATED) others don’t

(UNMYELINATED)

Myelin in CNS comes from Oligodendrocytes

Myelinated axons appear as white matter

Unmyelinated axons are gray matter

Can we fix it? Peripheral neurons are able to regenerate if damaged

Myelin sheath is surrounded by a tube of neurilemma

CNS neurons are not able to regenerate if damaged Not surrounded by neurilemma

More on Neurons Neurons can be classified based on structure

Multipolar-brain and SC Bipolar-eyes, nose, ears Unipolar-ganglia outside CNS

More on Neurons Neurons can be classified based on function:

Sensory Neurons- (afferent) carry impulses from body parts to brain or spinal cord (unipolar, some bipolar)

Interneurons- lie entirely within the brain or spinal cord (CNS); transmit impulses from one part of the brain or spinal cord to another. (Multipolar)

Motor Neurons- (efferent) carry impulses out of the brain or spinal cord to effectors (multipolar)

Neuroglial Cells Fill spaces, support neurons, provide structural frameworks,

produce myelin, and carry on phagocytosis.

Types: microglial, oligodendrocytes, astrocytes, ependymal cells, schwann cells