The Nervous and Muscular Systems…and the role of ATP

Overview of the Nervous System

General parts:

• The brain

• The spinal cord

• The nerves and sense organs

General functions:

• controls and coordinates body’s activities

• helps us sense and respond to changes in the environment

Functions Sensory Input: • Sensation of hot and cold via sensory nerves to the

brain • Response to external stimuli

Integration: • Data interpretation by the brain and spinal cord

• Sums up data and sends out impulses

Motor Output: • Signals (nerve impulses) from the brain and spinal cord

to the effectors (muscles, glands, organs) • Responses include muscle contractions, gland secretions, and

changes in organ function

Divisions of the Nervous System

The Central Nervous System (CNS):

• The brain and spinal cord

The Peripheral Nervous System (PNS):

• Consists of cranial and spinal nerves

Structure of a Neuron Cell body – contains the

nucleus and other organelles

Dendrites – receive signals from sensory receptors or other neurons

Axon – conducts nerve signals

– group together in a bundle and form a nerve

– axon bundle is called a tract in the CNS

Sensory Neuron

Where found: Outside of the brain and spinal cord (PNS)

Function:

bring sensory info from skin, muscles and organs to the spinal cord (CNS)

Sensory receptors

Sensory receptor

Long dendrites (called an

axon)

Cell Body

Short Axon leading to

spinal cord

Interneurons (Association Neurons)

Found: CNS only

Function:

Convey impulses between

various parts of the CNS

• Integrate messages

• Are involved in thinking, memory, and language processing

• Link other neurons

Sensory Neuron

Short dendrites (of

interneuron)

Cell Body

Short Axon leading

motor neuron

Motor Neurons (efferent) • Found: CNS and PNS

• Function:

– Carry nerves impulses from the CNS to the

muscles , glands and organs (effectors)

CNS

Short dendrites

Cell Body

Long Axon to effector

Neuromuscular junction – where the neuron meets a muscle

Steps of a nerve impulse from a neuron to a muscle

• Nerve impulse travels down axon.

• Calcium is released.

• Neurotransmitters stored in synaptic vesicles in the axon terminal.

• Neurotransmitters are released into synaptic cleft .

• Neurotransmitter binds to receptors on muscle cell.

• Impulse travels through muscle cell…

Types of Muscles

Skeletal Cardiac Smooth

Smooth Muscle

• Found in hollow parts of the body (stomach, intestines, blood vessels, bladder)

• Many mitochondria (needs lots of energy)

• Involuntary

• Does not fatigue easily

Cardiac Muscles

• Found in Heart

• Many mitochondria

• Involuntary rhythmic contractions

• Never rests

Skeletal Muscle

• Some more mitochondria than others

• Voluntary

• Attached to bone via tendons

• Over 600 in your body

Plasma membrane = sarcolemma

Cytoplasm = sarcoplasm

Mitochondria= where CR occurs

Endoplasmic Reticulum = sarcoplasmic reticulum

A skeletal muscle cell

Organization: Microscopic to macroscopic

• Myofibril – actin and myosin unit

• Muscle fiber – muscle cells with organelles

• Fascicle = bundle of muscle fibers

• Muscle = organ ( includes all above parts)

Sarcomere

• Protein filaments

– Thin filaments-Actin, Troponin, Tropomyosin

– Thick filaments-Myosin

• Contraction of a muscle occurs as the actin filaments move over the myosin filaments

How muscle contracts • ATP and Calcium are necessary

• Calcium binds to troponin, tropomyosin moves to reveal myosin head binding sites.

• Myosin heads bind to actin and pull inward • https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_cross-bridge_movement_during_muscle_contraction.html

Role of ATP in muscle contraction

Contraction = movement of actin over myosin

M line

Thick myosin without overlap of actin = H zone Middle of I band (actin protein attached) = Z line

Steps of Muscle Contraction

1. Impulse travels across sarcolemma and down t-tubules

2. SR releases calcium

3. Calcium binds to troponin proteins on actin

4. Tropomyosin proteins on actin move to reveal myosin head binding sites

5. Myosin heads bind to actin and pulls inward

6. Myosin heads detach from actin (requiring ATP)

Slow vs. Fast Slow twitch fibers: aerobic

• More endurance, high resistance to fatigue

• Helpful in long-distance running, biking, jogging, swimming

• Dark: many mitochondria

Fast twitch fibers: anaerobic

• Strength, quick fatigue

• Weight lifting, sprinting

• Light: few mitochondria