BIO 5, CH.14 - Nervous Tissue / Axon Regeneration

Central Nervous System (CNS)

includes the brain and spinal cord

Peripheral Nervous System (PNS)

includes the cranial nerves, spinal nerves, and ganglia

Brain (CNS)

receives & processes sensory information, initiates responses, stores, memories, generates thoughts & emotions

Spinal Cord (CNS)

conducts signals & from the brain, controls reflex activities

Sensory Neurons (PNS)

sensory organs to CNS

Motor Neurons (PNS)

CNS to muscles & glands

Somatic Nervous System

controls voluntary movements

Autonomic Nervous System

controls involuntary responses

Sympathetic Division (ANS)

“fight or flight”

Parasympathetic Division (ANS)

“rest or digest”

COLLECT Information

receptors in PNS detect changes in environment, pass information on to CNS

PROCESS AND EVALUATE Information

CNS determines required response

INITIATE Response

CNS initiates impulses that PNS carries to effectors (muscles or glands) to react to changes in environment

COLLECT

information

PROCESS & EVALUATE

information

INITIATE

response

Sensory Nervous System

detects stimuli & transmits information from receptors to the CNS

Sensory Nervous System: Somatic Sensory

sensory input that is consciously perceived from receptor (e.g., eyes, ears, & skin)

Sensory Nervous System: Visceral Sensory

sensory input that is not consciously perceived from receptors of blood vessles & internal organs (e.g., heart)

Motor Nervous System

imitates & transmits information from the CNS to effectors

Motor Nervous System: Somatic Motor

motor output that is consciously or voluntarily controlled; effector is skeletal muscle

Motor Nervous System: Automatic Motor

motor output that is consciously or is involuntarily controlled; effectors are cardiac muscle, smooth muscle, & glands

NEURONS (NERVE CELLS)

electrically excitable cells that initiate, transmit, and receive nerve impulses

GLIAL CELLS

NON-excitable cells that support

NEURON: characteristics

- High metabolic rate

- Excitable

- Extreme longevity

- Conductive (propagate electrical signal)

- Nonmitotic

Neuron Structure

• Neurons vary in shape, but most have:

• cell body

• dendrites

• axon

CELL BODY (soma)

center part

- nucleus & surrounding cytoplasm of a neuron (excluding its dendrites & axon)

– contains several organelles:

• nucleus with nucleolus

• mitochondria

• free ribosomes and rough endoplasmic reticulum (Nissl bodies)

AXON

away from the cell body

- transmits nerve impulses AWAY from the cell body and to other cells (OUTPUT)

• Neurons have either 1 axon or no axon (anaxonic)

– The region where the axon connects to the cell body is the axon hillock

DENDRITES

towards the cell body

- are short processes (INPUT), neuron process that conducts information to the cell body (input)

• Transfer signals TOWARD the cell body

Glial Cells

• Neuroglia (glial cells) protect and nourish neurons

• Found in both CNS and PNS

• Smaller and more numerous than neurons

• Capable of mitosis

• Brain tumors are more likely to be derived from glial cells than neuron

CNS (Central Nervous System) Glial Cells

four types of glial cells in CNS

Astrocytes (CNS)

helps form the blood-brain barrier (BBB), regulates tissue fluid composition, provides structural support & organization to CNS, replaces damaged neurons, assists with neuronal development, helps regulate synaptic transmission

Ependymal Cells (CNS)

lines ventricles of brain & central canal of spinal cord, assist in production & circulation of CSF

Microglial Cells (CNS)

defends against pathogens, removes debris, phagocytosis wastes

Oligodendrocytes (CNS)

myelinates & insulates CNS axons, allows faster nerve impulse conduction through the axon, wrap themselves around the axons like electrical tape wrapped around a wire

Satellite Cells

arranged around the neuron’s, regulate fluid composition around neuron cell bodies

Neurolemmocytes/Schwann Cells

wrap neuron’s axon, associated with PNS axons only, wrap an axon like electrical tape wraps a metal wire, produces myelin an insulator of electrical activity, similar in structure & function to oligodendrocytes

Myelination of Axons

• Myelin affects the ability of neurons to conduct nerve impulses (action potentials)

• Myelination is the process of wrapping the axon with a myelin sheath to electrically insulate it

• The glial cells involved are neurolemmocytes in the PNS and oligodendrocytes in the CNS

Synapses

specialized junctions between two neurons

– Some synapses are connections between a neuron and a muscle cell or a gland cell

Presynaptic Neuron

has synaptic knobs at axon endings for sending signal

Synaptic Cleft

narrow space between cells

Postsynaptic Neuron

receives signal