Bio 209 Ch 12

• Central Nervous System (CNS):
• - Brain
• - Spinal Cord
• Peripheral Nervous System (PNS):
• - Cranial nerves
• - Spinal Nerves
• - Sensory Receptors

• Sensory Function
• Integrative Function
• Motor Function

CNS: (1) Brain (2) Spinal cord

PNS: contains three divisions, Somatic – Autonomic – Enteric

• CNS:
• (1) Processes sensory information and initiates appropriate response
• (2) Initiates voluntary muscle contraction such as walking and picking up objects
• (3) Thoughts, emotions and memories

PNS:

• - Somatic: consists of sensory neurons that carry sensory information from (skin, skeletal muscle and tendons) and special sensory receptors (vision, smell, taste, hearing) to CNS fibers (these impulses consciously controlled and are voluntary)
• - Autonomic: consists of sensory neurons carrying info from autonomic sensory receptors (receptors in blood vessels and visceral organs) – motor neurons that carry nerve impulses to smooth muscle, cardiac muscle, glands, adipose tissue (generation of these impulses not normally consciously controlled and are involuntary)
• - Enteric (brain of the gut)

• Neurons
• Neuroglia

Are electrically excitable (respond to a stimulus by generating an action potential)

Change in the environment that is strong enough to result in an action potential

electrical signal that travels along the cell membrane of a neuron – there are generated by the flow of ions (mainly Na & K) between interstitial fluid (between cells) and intracellular fluid

Nucleus & Nucleolus

Cytoplasm: mitochondria, golgi apparatus, lysosomes, SER, ribosomes, Nissl Bodies (RER of neuron), cytoskeleton

Dendrites: short processes that receive info from other neurons and receptors

• Axon: propogates nerve impulse towards another neuron, muscle fiber or gland
• - Axon Hillock: cone shaped structure that connects axon to cell body
• - Trigger Zone: located in part of axon closest to axon hillock and generates action potentials

• Axon Terminals: form part of synapse
• - Synaptic End Bulbs: bulb like structures at tip of axon terminal and contains synaptic vesicles with neurotransmitter

Cell Body is the biosynthetic center of the neuron

• (1) Transport material from cell body (biosynthetic center) to axon of axon terminal
• (2) Transport substances from axon to cell body to be recycled

Mainly dendrites and one axon; can be found mainly in brain and spinal cord

One dendrite, one axon; can be found in retina, ear, olfactory area

Dendrite and axon fused together to form one process; mostly sensory receptors for touch, pressure, pain, temperature

mostly unipolar and some bipolar neurons; conducts action potential towards CNS through cranial and spinal nerves

mostly motor neurons; conducts action potential away from CNS to effectors (muscle/glands) through cranial and spinal nerves

mostly multipolar neurons: located between sensory and motor neurons

• (1) Neuroglia DO NOT exhibit electrical excitability (action potentials)
• (2) Neuroglia are smaller than neurons
• (3) Neuroglia replaces damaged neurons

have processes that surround capillaries - control chemical environment around neurons; help form BBB; BBB prevents harmful substances from entering CNS

in CNS; remove cellular debris, microbes, damaged nervous tissue

contain cilia - form CSF, assist in circulation of CSF

have processes that wrap around several axons to form myelin sheath of CNS neurons

located around neuron cell bodies in ganglia, control chemical environment of neurons

myelin sheath around axon of PNS neurons

Structure: plasma membrane of oligodendrocytes and Schwann cells; plasma membrace wraps around axon several times (like wrapping electrical tape around a wire)

Function: insulates axon and increases speed of nerve impulse

cluster of neuron cell bodies in CNS

cluster of neuron cell bodies in PNS

bundle of axons in CNS

bundle of axons in PNS; most nerves supplying skeletal muscles are myelinated

primarily myelinated axons that gives it its white color

neuroglia, neuron cell bodies, dendrites, unmyelinated axons, axon terminals

communication over long distances generated in axons

communication over short distances by stimulus to neuron in dendrites, and to neuron cell body then to axon hillock

randomly opens and closes

open and closes in response to a change in membrane potential

open and close in response to chemical stimuli (neurotransmitters & hormones)

opens and closes in response to mechanical stimulation such as vibration, stretch or touch. These receptors are found in skin and in internal organs

• (1) Differences in concentration of ions across plasma membrane:
• - ECF has more Na than ICF
• - ICF has more K than ECF
• - More K leave cells through
• Leakage-Channels than Na entering à More positive charges leave the cell à Inside of cells becomes slightly negative
• (2) Inability of most anions to leave the cell
• (3) Na/K ATPase
• - Maintains the difference in Na and K ion concentrations

change in membrane potential that makes plasma membrane more polarized (inside more negative) or less polarized (inside less negative); caused by opening of ligand-gated/mechanically gated ion channels in dendrites

less polarized (inside less negative)

more polarized (inside more negative)

• Amplitude of Graded Potential varies according to:
• (1) Intensity of stimulus
• (2) Intensity of stimulus determines number of ion channels that open and the length of time ion channels open

Exhibited by Graded Potentials in which results in a graded potential decreasing in amplitude and dying out a few mm from the point of origin (point where stimulus is applied)

graded-potentials that occur after neurotransmitter binds to receptor on plasma membrane

graded-potentials that occur in sensory receptors and sensory neurons

• (1) Stimulus causes depolarizing graded-potential in dendrites
• (2) Depolarizing graded-potential travels across neuron
• (3) Action-Potential occurs if membrane potential at trigger zone is depolarized to threshold (-55mV) – Depolarization to threshold opens voltage-gated Na channels à Action Potential
• (4) Action-Potential travels down axon

region where communication occurs between two neurons or between a neuron, muscle, or gland

neuron sending signal

neuron receiving signal

• - Current spreads directly between adjacent cells connections between
• plasma membranes (Gap Junctions)
• - Advantages:
• (1) Faster than chemical synapses
• (2) Can sync activity of group of neurons or muscle fibers
• (3) Allows two-way transmission of information whereas chemical synapses transfers info in one direction only