Nervous System

Introduction

• Vast collection of cells that gather information and help coordinate body functions to maintain homeostasis

• Nervous tissue consists of masses of nerve cells or neurons.

• Neurons are the structural and functional units of the nervous system

Introduction

• Organs of the nervous system can be divided into two categories– Central nervous system (CNS)• Consists of the brain and spinal cord

– Peripheral nervous system (PNS)• Consists of nerves(peripheral nerves) that connects the

CNS to the rest of the body• Cranial and spinal nerves

General Functions of the Nervous System

• Sensory function- derives from the sensory receptors at the ends of peripheral nerves– These receptors gather information by detecting

changes– Convert environmental information into nerve

impulses• Integrative function- takes these nerve

impulses, brings them together and creates senses

General Functions of the Nervous System

• Motor function-act on these senses using effectors– Effectors are structures outside of the nervous

system, such as muscles and glands• Can be divided into two categories– Somatic nervous system• Controls the skeletal muscle

– Autonomic nervous system• Controls effectors that are involuntary

Neuroglial Cells

• Fill spaces, provide structural framework, produce myelin, and carry on phagocytosis

• Neurons cannot exist without these cells

Neurological Cells

• Four main types found in the CNS– Ependymal cells-forms membranes– Microglial cells-eat bacterial cells – Oligodendrocytes-provide myelin– Astrocytes-provide structural support

• One other type is found in the PNS– Schwann cells-form myelin sheath around axons

Neurological Cells

Neurons

• Vary greatly in size and shape, but all have common features– Cell body (soma)– Dendrites- receives signals – Axon-conducts nerve impulses away • Myelinated-with myelin sheath• Unmyelinated-without myelin sheath

– Axon terminal

Neuron

Neurons

• Neurons are classified in several different ways– On the basis of structural differences• Multipolar neurons-having many processes arising from

the cell body, only one is an axon• Bipolar-having two processes, only one is an axon the

other is a dendrite• Unipolar-having a single process that divides into two

branches.

Neurons

Neurons

• These can also be classified on the basis of functional differences– Sensory neurons-carry nerve impulses from the

peripheral parts of the body to the brain or spinal cord

– Interneurons-lie entirely within the brain or spinal cord. These neurons direct impulses to different parts of the brain or spinal cord

– Motor neurons-carry nerve impulses out of the brain or spinal cord to effectors