Reflexes Flashcards
Spinal Cord structure
Column of nervous tissues running up the back. Surrounded by spine for protection and at intervals along the spinal cord, pairs of neurones emerge.
Knee-Jerk reflex - explain how it is actually brought about:
Tapping beneath the patella (knee-bone) with a stick, causes you to instinctvely kick.
This stretches the patellar tendon and stimulates the extensor msuscle on top of the thigh to contract.
At the same time, a relay neurone inhibits the motor neurone of the flexor muscle causing it to relax.
What may be indicated if there is an absence of the knee-jerk reflex or even multiple ossciliations?
Absence of knee-jerk reflex: nervous problems
Multiple ossciliations: cerebellar disease
Blinking reflex - how its brought about?
Cornea has to be stimulated, due to for example, it being touched/dust flying into eye.
So the cornea recieves sensory information from the fifth cranial nerve via sensory neurones. This then travels through relay neurones in the lower brain stem. Impulses are then sent along branches of the motor neurone (seventh cranial nerve) to initiate a motor response to close the eyelids.
Reflex initiates a consensual response - to close both the eyelids.
3 essential aspects of reflexes:
1) Very fast - reflex arc is short with only one or two synapses.
2) Involuntary responses - decision making and active areas of the brain not involved.
3) Not having to be learnt - present at birth and therefore provide immediate protection.
Skeletal muscle - what is it?
Make up bulk of body muscle tissue.
Cells responsible for movement, such as biceps or triceps.
Cardiac muscle
Myogenic cells meaning that they contract without the need for nervous stimulus, causing heart to beat in a regular rhythm,
Involuntary muscle
Muscles under unconscious control - we cant move it if we want to (still require a nervous stimulus though - unlike cardiac muscle). Found in walls of blood vessels and digestive tract - for example, those used in peristalsis to move food through the gut.
What is the sarcolemma - what role does it have in the structure of a skeletal muscle fibre?
Why is this important?
The plasma membrane that surrounds the bundles of muscle fibres.
Parts of the sarcolemma fold inwards known as T/transverse tubules which help spread electrical impulses throughout the sarcoplasm. This ensures that the WHOLE OF THE MUSCLE FIBRES recieves the impulse to contract at the same time. (no delayed contractions of certain fibres vs not)
What are myofibrils?
Long cylindrical organelles made out of protiein and specialised for contraction. They are lined up in parallel so that they generate maximum force when they all contract together.
Made up of two types of filament s- actin and myosin
Why do muscle fibres have a lot of mitchondria?
Mitochondria is the site of aerobic respiration that releases energy which is needed for the muscles to contract with force
Sarcoplasmic reticulum function in muscle fibres?
Essentially is a modified version of the endoplasmic reticulum and extends throughout the muscle fibre.
Contains calcium ions needed for muscle contraction.
Two types of filaments in myofibrils?
Actin - Thinner filament, consists of two strands twisted around each other.
Myosin - Thicker filament, consists of long rod-shaped fibres with bulbous heads that project to one side.
Structure of a myofibril - e.g. from a picture of a transverse section
1) Light bands
2) Dark bands
3) Z-line
Alternating light and dark bands.
Light bands - where myosin and actin do not overlap - Isotopic (I) bands
Dark bands - presence of thick myosin filaments - edges particularly dark as myosin is overlapped with actin (Anisotropic (A) bands)
Z-line - line found at the centre of each light band, the distance between adjacent Z lines (so obv in adjacent light bands) is called the sarcomere. Sarcomere is the functional unit of a myofibril - when a muscle contracts, the sarcomere shortens.
H-zone - lighter (relative to edges where overlap of actin and myosin) coloured region in a dark band where only thick myosin filaments are present- when muscle contracts. the H-zone decreases
What happens to it when a muscle contracts
Sarcomere?
H-zone?
Sarcomere is the functional unit of a myofibril - when a muscle contracts, the sarcomere shortens.
The H zone decreases (in size), when a muscle contracts
Slow-twitch muscle fibres:
How they gain energy?
What they used for?
Where are they found?
Fibres contract slowly - less powerful contractions but over a longer period.
Gain energy from aerobic respiration
Rich in myoglobin - a bright red protein which stores oxgyen, making fibres appear red.
Used for endurance activities as they do not tire easily.
Found in large proportions in muscles that help to maintain posture and body upright such as that in the back and calf muscle activity.
Fast-twitch muscle fibres:
How they gain energy?
What they used for?
Where are they found?
Fibres contract quicly - more powerful contractions but over a shorter period.
Gain energy from anaerobic respiration
Low levels of myoglobin - so pale coloured
Store creatine phosphate - a molecule that can rapidly generate ATP from ADP in anaerobic conditions.
Found in large proportions in muscles which need short intense bursts of activity such as biceps and eyes
Structure of a muscle fibre:
One large shared cytoplasm (sarcoplasm) - no junctions/gaps in between cells that mean no weak points - so muscle is stronger.
Embroynic muscle cells are fused together and the muscle fibres contain nuclei that are larger than normal cells.
Skeletal muscle structure?
Bundles of muscle fibres which are enclosed in a plasma membrane called a sarcolemma.
Muscles showing cross striations are known as striated or striped muscles. The fibres are tubed (long cylindrical structure) and multinucleated (several larger-than-normal nuclei)
Cardiac muscle structure?
Shows striations but they are much fainter than those in skeletal muscles. Fibres are BRANCHED and uninucleated (each fibre is a single muscle cell that contains a single nucleus)
Involuntary muscle structure
Muscles showing no cross-striations - they are non-striated or unstriped muscles. Fibres are spindle shaped and uninucleated.
What actually are striations?
Stripes/Sractches/Grooves on a muscle fibre.
Sliding Filament model - what is it briefly and what roughly does it consist of?
The model by which muscle contracts
During muscle contraction, the action and myosin microfilaments in the myofibril have to slide past each other.
Sliding filament model:
What happens during contraction?
1) Light band
2) Z lines
3) H zone
4) Dark band
Myosin filaments pull the actin filaments inwards towards the centre of the sarcomere, which results in:
1) Light band becoming narrower
2) Z lines moving closer together, shortening the sarcomere
3) H zone becoming narrower
Dark band remains the same width, as the myosin filaments themselves have not shortened, but now overlap the actin filaments by a greater amount.
The simulatenous contraction of lots of sarcomeres means that myofibrils and muscle fibres contract. This results in enough force to pull on a bone and cause movement. When sarcomeres return back to their orginal length, the muscle relaxes.
