Lecture 2Lecture 2Neurons, Muscles and Motor Neurons, Muscles and Motor

UnitsUnits

Voluntary movement begins....Voluntary movement begins....

BrainBrain

Spinal cordSpinal cord

Motor nervesMotor nerves

MusclesMuscles

M o to r sys tem M u scu loske le ta lS ys tem

S e n so ry sys tem

M o vem e nt

The Nervous SystemThe Nervous System

Central nervous Central nervous System (CNS).System (CNS).

BrainBrain Spinal cordSpinal cord

Peripheral Nervous Peripheral Nervous System (PNS).System (PNS).

Everything elseEverything else

Somatic AutonomicSomatic Autonomic

Nervous system cellsNervous system cells

NeuronNeuron

Basic unit of the NSBasic unit of the NS

GlialGlial

Support, myelin, Support, myelin, scavengers.scavengers.

The neuron:The neuron:

Consists of three major parts:Consists of three major parts: Soma or cell body (nucleus).Soma or cell body (nucleus). Axon (carries the output signals Axon (carries the output signals

generated by the cell).generated by the cell). Dendrites (inputs into the cells).Dendrites (inputs into the cells).

How is the info. being How is the info. being transferred from cell to transferred from cell to

cell?cell?

Synapses....Synapses....

Connections to other cells, consist of Connections to other cells, consist of three main components:three main components:

Presynaptic membranePresynaptic membrane Postsynaptic membranePostsynaptic membrane Synaptic cleftSynaptic cleft

Presynaptic membrane

Synaptic cleft

Postsynaptic membrane

Synaptic vesicles

Neurotransmitter

Neuron to neuron synaptic Neuron to neuron synaptic transmission uses chemical transmission uses chemical substances called substances called neurotransmittersneurotransmitters..

Signal transportation...Signal transportation...

Action potentialAction potential

Transmission of information Transmission of information through the NS in the form of through the NS in the form of electrical impulse.electrical impulse.

StimulusStimulus

DepolarizationDepolarization

HyperpolarizationHyperpolarization

Resting

Potential

Resting

Potential

Speed of conduction with regard Speed of conduction with regard to the neural signalto the neural signal Higher speed along thick neural Higher speed along thick neural

fibers.fibers. Higher speed in myelin covered Higher speed in myelin covered

fibers.fibers.

Primary Afferent / Sensory AxonsPrimary Afferent / Sensory Axons

One Presynaptic action One Presynaptic action potential is usually unable to potential is usually unable to force the membrane of the force the membrane of the postsynaptic neuron to postsynaptic neuron to generate an action potential - generate an action potential - subthreshold.subthreshold.

(Muscle-exception, will always stimulate the muscles due to the high voltage).

How do we get an action potential?How do we get an action potential?

In order to generate an action potential, In order to generate an action potential, the Postsynaptic membrane requires the Postsynaptic membrane requires to sum up the effects of a number of to sum up the effects of a number of signals.signals.

This is what we call This is what we call summationsummation..

There are two types of summation:There are two types of summation: Temporal summationTemporal summation Spatial summationSpatial summation

Temporal summationTemporal summation An accumulative effect on the An accumulative effect on the

membrane potential of a postsynaptic membrane potential of a postsynaptic cell; caused by chemical transmissions cell; caused by chemical transmissions from one or more synaptic terminals from one or more synaptic terminals occuring so occuring so close together in timeclose together in time that that each postsynaptic potential affects the each postsynaptic potential affects the membrane before the voltage has membrane before the voltage has returned to the resting potential after the returned to the resting potential after the previous stimulation.previous stimulation.

Spatial summationSpatial summation

An accumulative effect on the An accumulative effect on the membrane potential of a membrane potential of a postsynaptic cell, caused by postsynaptic cell, caused by several several different synaptic terminals different synaptic terminals stimulating a postsynaptic cell stimulating a postsynaptic cell membrane.membrane.

Muscles...Muscles...

Muscles....Muscles....

Contractile components:Contractile components:

MyofibrilMyofibril

Muscle fiberMuscle fiber

Muscle fasciclesMuscle fascicles Elastic components:Elastic components:

TendonTendon

Neuromuscular synapse/junctionNeuromuscular synapse/junction

A region of contact between a single A region of contact between a single Presynaptic fiber and a muscle fiber.Presynaptic fiber and a muscle fiber.

The two fibers are very close to each The two fibers are very close to each

other but no direct contact.other but no direct contact.

Motor UnitMotor Unit

The smallest functional unit of the The smallest functional unit of the neuromotor system. neuromotor system.

Typically, each muscle fiber is Typically, each muscle fiber is innervated by only one axon branch.innervated by only one axon branch.

The motorneuron and the muscle fibers The motorneuron and the muscle fibers it innervates are called a motor unit.it innervates are called a motor unit.

Types of contractionTypes of contraction

A single action potential to a A single action potential to a muscle that responds with one muscle that responds with one contraction is a contraction is a TWITCH.TWITCH.

Many action potentials happen at Many action potentials happen at the same time, contraction is the same time, contraction is sustained, a sustained, a TETANUS TETANUS is is observed.observed.

Muscle contractionMuscle contraction

Decision by the CNS for muscle Decision by the CNS for muscle contractioncontraction

Signal is sent to neurons in the spinal Signal is sent to neurons in the spinal cordcord

Signal is propagated through the axons Signal is propagated through the axons to appropriate musclesto appropriate muscles

Muscles are activatedMuscles are activated

Muscle contractionMuscle contraction

CNS command to contract

Signal is sent to the spinal cord

Signal propagated to muscles via axons

Muscles are activated