MUSCLE & NERVOUS TISSUE

What is muscle tissue made up of?

Myocytes (muscle cells/fibres)

What are the three types of muscle in the body?

Skeletal muscle, smooth muscle and cardiac muscle

What are the roles of muscle tissue?

Produces body movements, maintains posture, and generates heat

What percentage of the tissue mass in the body does muscle make up?

Up to 50%

What kind of control are skeletal muscles under?

Voluntary/conscious control

What are the functions of skeletal muscle tissue?

Motion, posture, heat production, protection

What are muscle cells called?

Myocytes

What do muscle cells look like?

They are long and cylindrical, and have multiple peripheral nuclei

What is the longest muscle in the body and where is it?

Sartorius muscle, located in the leg, up to 60cm

What is the shortest muscle in the body and where is it?

Stapedius muscle, in the ear, up to 1.25mm

How are skeletal muscles usually attached to bone?

Via tendons

What do the striations in myocytes come from?

The arrangement of myofibrils in the muscle cell

What is the arrangement of myofibrils in myocytes?

They are long cylindrical structures that span the whole length of muscle cells

What are the two types of myofilaments that myofibrils are composed of?

Thin = actin, thick = myosin

Do myofilaments span the whole length of a myofibril?

No, they are arranged into repeating sections

Do myofibrils span the whole length of the sarcoplasm of a muscle fibre?

Yes

How are myofilaments arranged in myofibrils?

In repeating sections called sarcomeres

What are the striations of skeletal muscle fibres due to?

They are due to the highly organised arrangement of myofibrils within the cells

What is the basic functional unit of a myofibril?

Sarcomeres

What are sarcomeres separated by?

Z discs

What are the parts of a sarcomere?

A band, I band, H zone, M line, Z disc, Titin

What is the A band in a sarcomere?

The dark middle part that has all the thick filaments (myosin)

What is the I band in a sarcomere?

Light part of the sarcomere that is only comprised of thin filaments (actin)

What is the H zone in a sarcomere?

Area with only thick filaments

What is the M line in a sarcomere?

The middle of the sarcomere where the thick filaments attach, holding them together

What are Z discs in a sarcomere?

They pass through the centre of the I band and separate sarcomeres, made up of actinins (proteins) which link myofilaments of adjacent sarcomeres

What is titin in a sarcomere?

A molecular spring which links the Z disc to the M line and provides resting tension to the I band

What surrounds the anatomical muscle and why?

Epimysium, to prevent muscles sticking to each other as they move over each other, therefore improving the efficiency of contraction

What is a fascicle?

A group of 10-100 muscle fibres (cells)

What surrounds fascicles?

Perimysium

What surrounds a muscle fibre and why?

Endomysium, as it is a layer where capillaries and nerves run to make muscles contract

What does endomysium do for a muscle fibre?

Surrounds the fibre, providing a layer for capillaries and nerves, outside the cell membrane

What is sarcolemma?

The plasma membrane of a muscle fibre

What fills the sarcoplasm of a muscle fibre?

Myofibrils

What is sarcoplasm?

The cytoplasm of myocytes

What do cardiac myocytes look like?

A single central nucleus and are striated and branched, and they join end to end through intercalated discs

Is cardiac tissue involved in voluntary or involuntary movement?

Involuntary

What are intercalated discs?

Transverse thickenings of plasma membrane, containing desmosomes and gap junctions

What myofilaments do cardiac myocytes have?

Actin and myosin myofilaments

How do cardiac myocytes join?

They join at branch points with intercalated discs

What cell junctions do cardiac myocytes have?

A combination of desmosomes and gap junctions

What purpose do desmosomes in cardiac muscles serve?

They prevent cell separation by binding onto intermediate filaments, and provide adhesion in contraction

What purpose do gap junctions in cardiac muscle serve?

They provide a route for quick communication between cells via electrical muscle action potentials so they contract in coordination

What are purkinje fibres?

Specialised muscle cells that conduct electrical activity around the heart, that have less myofibrils and more specialised gap junctions

Where is cardiac muscle tissue found?

In the heart wall

Does smooth muscle have striations?

No

Where is smooth muscle tissue found?

In the walls of hollow internal structures such as the intestine (for peristalsis) and blood vessel walls (for constriction), and the iris of the eye, airways to lungs, stomach, gallbladder, urinary bladder and uterus

What are smooth muscle myocytes made up of?

Actin thin filament attached to dense bodies actinin which acts like Z discs. Intermediate filaments also attach to these dense bodies

What do smooth muscle myocytes look like?

Small, short and spindle shaped (wide in middle thin at ends), single central nucleus

Are smooth muscle tissues involved in voluntary or involuntary movement?

They are involved in involuntary movement

What does the shape of smooth muscle myocytes aid them to do?

Helps them pack around circular shapes

How do smooth muscle myocytes contract?

Tension is transmitted to the intermediate filaments (which don't contract) and the cell twists as it contracts about these 'stable rods'

What cell junctions do smooth muscle myocytes have and can this vary?

Gap junctions, the amount of which is dependent on the location in the body i.e. how much communication between cells is required. Where they are absent (e.g. iris of eye), smooth muscle fibres contract individually

What are the functions of smooth muscle tissue?

Motion - constriction of blood vessels and airways, propulsion of foods through gastrointestinal tract, contraction of urinary bladder and uterus

What are the two components of the nervous system?

CNS and PNS

What is the nervous system responsible for and what are its other functions?

Behaviour, perception and memory, and it helps to maintain homeostasis and initiates voluntary movements

What three processes does the nervous system carry out its functions through?

Sensory, integration and motor

What is the sensory process of the nervous system?

Detection of internal and external stimuli and transfer of them to the CNS

What is the integrative process of the nervous system?

Analysis and storing of information

What is the motor process of the nervous system?

Stimulation of effectors such as muscles and glands through the PNS

What is the CNS made up of?

The brain and spinal cord and optic nerve

What are the two divisions of the PNS?

Sensory/afferent division and motor/efferent division

What is the sensory/afferent division of the PNS?

Carries information to the CNS

What is the motor/efferent division of the PNS?

Carries information from the CNS to organs, via muscles and glands

What is the role of the CNS?

It is the control centre of the nervous system and can control other systems for short periods of time.

What is the role of the brain in the CNS?

It is the control centre of the CNS and controls voluntary and involuntary activities and plays a role in integration of complex activities

What is the role of the spinal cord in the CNS?

Relays information to/from the brain and has a role in integration of less complex activities such as the reflex arc

What components of the nervous system are the special senses part of?

All of them are part of the CNS and PNS (except optic nerve)

What is the exception to where the special senses belong in the nervous system?

The optic nerve only belongs to the CNS

What do the special senses do?

They provide sensory information regarding hearing, sight, sound, smell, taste and equilibrium

What are nerve cells called?

Neurons

What are neurons involved in?

Transmission of action potentials

What is the general structure of a neuron?

They have a cell body with dendrites branching out from it and axons that conduct action potentials

What do axons do?

They conduct action potentials

What happens if the oxygen supply to neurons is cut off?

They die rapidly

Do neurons divide?

No

What are the four types of neurons?

Multipolar neurons, unipolar neurons, bipolar neurons and anaxonic neurons

What type of neurons innervate skeletal muscles?

Multipolar neurons

What is the most common neuron found in the CNS?

Multipolar neurons

What is the structure of a multipolar neuron?

Two or more dendrites and a single axon

What is the structure of a unipolar neuron?

Dendrites and axons are continuous and the cell body is located off to the side

What is the cell body of a neuron called?

Soma

What kind of neuron are most sensory neurons?

Unipolar neurons

What is the structure of a bipolar neuron?

They have two processes, one dendrite and one axon with the cell body (soma) found between the dendrite and axon

Where are bipolar neurons found?

In the special sense organs involved in sight smell and hearing

Where are anaxonic neurons found?

In special sense organs and the brain

What is known about anaxonic neurons?

They are rare and poorly understood

What are neuroglia?

Neuroglia are supporting cells found in the PNS and CNS

Can neuroglia divide?

Yes

Which is more numerous - neuroglia or neurons?

Neuroglia

Which is larger - neuroglia or neurons?

Neurons

Do neuroglia transmit action potentials?

No

What is an action potential?

A rapid change in membrane potential that propagates along a nerve cell or muscle fibre

What are the functions of neuroglia?

Involvement in defence, undertaking phagocytosis, providing nutrients to neurons, part of the physical structure of nervous tissue, involvement in repair, regulation of interstitial fluid of the nervous tissue

What are the four types of CNS neuroglia?

Astrocytes, microglia, ependymal cells, oligodendrocytes

What are the two types of PNS neuroglia?

Schwann cells, satellite cells

What structure does an astrocyte have?

Star shaped

What is a network of astrocytes called?

Syncytium

What is the purpose of astrocytes?

Support neurons, form BBB, help maintain chemical environment (e.g. potassium concentration), absorb excess neurotransmitters, conduit for passage of nutrients/substances between capillaries and neurons; in embryo secrete chemicals that regulate growth, migration, and interconnection among neurons in brain

How do astrocytes communicate?

Through gliotransmitters such as glutamate