Performs three basic continuous functions: Performs three basic continuous functions

Performs three basic continuous functions:

• Performs three basic continuous functions:

• Sensory input
• Integration
• Motor output

Sensory Receptors collect information from the outside environment.

• Sensory Receptors collect information from the outside environment.

Input is interpreted and linked to appropriate responses

• Input is interpreted and linked to appropriate responses

• Accomplished by the CNS (central nervous system)

• Brain
• Spinal cord

Signal conduction from CNS to effector cells in PNS (peripheral nervous system)

• Signal conduction from CNS to effector cells in PNS (peripheral nervous system)

• CNS is connected to effector cells via neurons, or nerve cells

PNS

• PNS

The NEURON, or nerve cell is the functional unit of the nervous system.

• The NEURON, or nerve cell is the functional unit of the nervous system.

• Composed of cell body, dendrites, axon, myelin sheath, synaptic terminals (bulbs)

Dendrites: receive afferent signals, incoming from other neurons or receptors

• Dendrites: receive afferent signals, incoming from other neurons or receptors

• Axon: only one per neuron; efferent pathway to other neuron or an effector cell (muscle, gland)

• Myelin sheath: lipid layer that insulates axon; produced by Schwann cells.

• Synaptic Terminals (bulbs): transmit signals from axon by release of neurotransmitters (Ach)

• Synaptic cleft (synapse): site of contact between two neurons or neuron and effector

• Postsynaptic cell: the receiver.

GLIA =“glue”

• GLIA =“glue”

• Used to believe they were wholly supportive, new research says not!

• Provide nutrition and protection.

• Lead neurons from neural tube along pathway in embryonic development.

Astrocytes: form connections between capillaries and neurons for feeding and waste disposal; in brain, they form tight junctions which form the blood-brain barrier.

• Astrocytes: form connections between capillaries and neurons for feeding and waste disposal; in brain, they form tight junctions which form the blood-brain barrier.

• Microglial cells: immune system cells which engulf microbes in the brain; alcohol kills microglial cells in fetuses.

• Oligodendrocytes (CNS) and Schwann Cells (PNS): form around axons like burritos; insulate electrical impulses and speed up nerve signal transduction.

All cells have a membrane potential, a difference in charge between inside and outside. Developed 2 weeks post conception, maintained through life.

• All cells have a membrane potential, a difference in charge between inside and outside. Developed 2 weeks post conception, maintained through life.

• The resting potential of an unstimulated nerve cell is about -70mV; negative inside the cell.

• The resting membrane potential is maintained by the Sodium-Potassium Pump.

• Neurons have a 50X greater permeability to K+ than Na+.

Cells in the body like muscle and nerve cells can create large changes in their membrane potentials.

• Cells in the body like muscle and nerve cells can create large changes in their membrane potentials.

• Environmental stimuli can cause these cells to alter their membrane potential, possibly causing an action potential.

Stimulus causes Na+ gates to open.

• Stimulus causes Na+ gates to open.

• Na+ influx changes membrane potential.

• If Na+ influx is great enough to achieve threshold potential (-50mV), then all Na+ gates open.

• “All or none” phenomenon…at threshold, all gates will be opened (below threshold, no extra gates will open) and stimulus is transmitted.

• Additional Na+ influx causes depolarization of membrane (action potential).

• K+ channels remain closed. Cell becomes positive.

Repolarization begins when K+ gates open and Na+ gates are closed. (~ +50mV)

• Repolarization begins when K+ gates open and Na+ gates are closed. (~ +50mV)

• K+ ions leave the cell, causing the interior to become more negative.

• BUT…The ions are in reversed concentrations!

• When K+ gates finally close, there is slightly more K+ outside than inside… hyperpolarization.

• Refractory period returns ions to resting state.

• Sodium-Potassium pump restores resting potential…no stimuli can be transmitted during this phase…the neuron is BUSY!

• Campbell p. 1020

All motor neurons are associated with muscle fibers at their peripheral end…the neuromuscular junction.

• All motor neurons are associated with muscle fibers at their peripheral end…the neuromuscular junction.

• There is a space between a neuron and a muscle fiber…the synaptic cleft.

• The depolarization wave cannot pass across the cleft!

Cardiac…found only in the heart; striated; involuntary

• Cardiac…found only in the heart; striated; involuntary

• Smooth…lines internal organs…digestive tract, blood vessels, rep. tract, bladder; not striated; involuntary.

• Skeletal…attaches to skeleton; striated; voluntary; multinucleate

Skeletal muscle is striated

• Skeletal muscle is striated

• Individual units are called sarcomeres.

• Thin filaments – actin

• Thick filaments –myosin

The depolarization wave in the neuron cannot traverse the synaptic cleft.

• The depolarization wave in the neuron cannot traverse the synaptic cleft.

• When action potential reaches the synaptic end bulb, Ca++ in the cleft flows into the bulbs.

• This calcium causes vesicles filled with neurotransmitters (acetylcholine) to migrate to the neural membrane.

The vesicles fuse with the cell membrane and exocytose their contents into the synaptic cleft.

• The vesicles fuse with the cell membrane and exocytose their contents into the synaptic cleft.

• Receptors on sarcolemma bind acetylcholine causing gated Na+ channels to open. As Na+ comes into the sarcoplasm, what happens?!

• DEPOLARIZATION !

The depolarization wave (DW) passes across the sarcolemma which extends into the muscle fiber via the T-tubules.

• The depolarization wave (DW) passes across the sarcolemma which extends into the muscle fiber via the T-tubules.

• T-tubules have close associations with the sarcoplasmic reticulum (SR), the Ca++ warehouse.

• The DW opens gated Ca++ channels allowing Ca++ to flow into the sarcoplasm…this is the important part!!!!

Ca++ binds the troponin complex.

• Ca++ binds the troponin complex.

• Once troponin is removed, the tropomyosin shifts away from the myosin binding sites.

• Ca++ serves as an enzyme cofactor with myosin and they become ATPase!

• The ATP is broken down into ADP and Pi. This allows myosin to bind to the actin filaments and contract the filament to the center of the sarcomere.

The binding of the acetylcholine receptors on the sarcolemma signals the release of acetylcholinesterase from the sarcolemma.

• The binding of the acetylcholine receptors on the sarcolemma signals the release of acetylcholinesterase from the sarcolemma.

• This enzyme breaks down acetylcholine in the synaptic cleft.

• How do you get the contraction to continue?

The myostatin gene is effectively blocked by being mistranscribed (it’s truncated)…leads to “double-muscled” animal.

• The myostatin gene is effectively blocked by being mistranscribed (it’s truncated)…leads to “double-muscled” animal.

Negative Feedback Control (depends on four detector types so that the CNS knows what the muscles are doing and can make adjustments accordingly)

• Negative Feedback Control (depends on four detector types so that the CNS knows what the muscles are doing and can make adjustments accordingly)

• •     Muscle spindles (so-called stretch receptors) – actually length detectors

• •     Golgi tendon organs – detectors of tension in tendons

• •     Joint angle receptors – indicate the angle of a joint

• •     Skin stretch and compression receptors – give information about how the skin is deformed around a joint

The Function of the Sympathetic Nervous System and Wartime…

• The Function of the Sympathetic Nervous System and Wartime…