Reflexes - Module 5 Flashcards
What is a reflex action?
Involuntary response to a sensory stimulus
What is a reflex arc?
Pathway of neurones involved in reflex action
What is the 4 step pathway of a reflex arc?
- Receptor - detects stimuli and starts action potential in sensory neurone
- Sensory neurone - carries impulse to spinal cord
- Relay neurone - connects sensory to motor neurone in spinal cord/ brain
- Monitor neurone - carries impulse to effector to carry out response
What is a withdrawal reflex?
Before the Brian realises, muscles have pulled away form danger
Describe the structure of the spinal cord
It is a column of nervous tissues protected by spine
Pairs of neurones emerge at intervals
What are the 4 importance features of reflexes for survival?
- Involuntary responses - doesn’t overload brain with response that is always the same
- Don’t have to be learnt - present from birth and provide immediate protection
- Extremely fast - reflex arc is short 1 or 2 synapses
- Many reflexes are every day actions like balance
How is the blink reaction used by doctors?
It is used to determine weather the lower brain stem is still functioning and subsequently weather someone is Brian dead
When does the blinking relax occur?
When the Cornea is stimulated and irritated
What is the purpose of the blink reaction?
To stop the damage of the Cornea
On what two other occasions do blink reflexes occur?
- Loud sound
- Very bright light
What is the optical reflex?
The blink reaction to very bright light to protect lens and retina
Why is the blink reaction a cranial reflex?
It occurs in the brain not the spinal cord
Describe the blinking reflex pathway
- Stimulus - something touches the cornea
- Receptors - sensory nerve endings detect stimulus and send impulse along sensory neurone
- CNS - impulse is received from sensory neurone and passed from relay neurone to motor neurone
- Effector - motor neurone sends impulse to effectors, in this case the muscle causing the eye to close
- The response to close the eye is generated
Describe the knee jerk reflex
- Stimulus - the quadricep muscle is stretched
- Receptors - stretch receipts detect stimulus and send a nerve impulse down sensory neurone
- CNS - sensory neurone communicates directly with motor neurone in spinal cord
- Effectors - motor neurone carries impulse to quadriceps muscle
- Response is quadricep muscle contracts so the lower leg moves forward quickly
What is the function of the knee jerk reflex?
Works to quickly straighten leg if body detects stretch in quadriceps maintains posture and balance
What is the 3 types of muscle?
Skeletal
Involuntary
Cardiac
What is the role of skeletal muscle?
Movement of the body
Is skeletal muscle conscious or involuntary?
Conscious
What is the speed and length of skeletal muscle contractions?
Rapid and short
What is the arrangement of fibres in skeletal muscle?
Striated and regularly arranged so muscle contracts in once direction
Are skeletal muscle cells uninucleate or multinucleate?
Multinucleated
Is cardiac muscle involuntary or conscious?
Involuntary
What is the structure of cardiac muscle?
Specialised striated and cells branch and interconnect
What is the speed and length of cardiac muscle contractions?
Intermediate speed and length
Are cardiac muscle fibres multinucleated or uninucleated?
Uninucleate
What is the structure of involuntary muscles?
Non striated and have no regular arrangement
What is the speed and length of contractions in involuntary muscles?
Long and slow contractions
Are involuntary muscle fibres uninucleate or multunucleate?
Uninucleate
What is sarcolemma?
The membrane that encloses the muscle fibre
Why do skeletal muscles have multiple nuclei?
They are much longer than normal cells and are formed from lots of embryonic muscle cells fusing together
What is the sarcoplasm?
Shared cytoplasm within muscle fibres
What are T-tubules?
Parts of the sarcolemma that fold inwards to spread electrical impulses evenly across sarcoplasm
What is the role of T-tubules?
To ensure electrical impulses spread across muscle fibres evenly
Why to muscle fibres have lots of mitochondria?
To provide ATP for muscle contraction
What is special about the endoplasmic reticulum in muscle fibres?
They have the sarcoplasmic reticulum which is a modified version that contains calcium ions
What are myofibrils?
Long cylindrical organelles specialised for contraction
Why are myofibrils aligned parallel?
To provide maximum force when they contracts as alone they have no power
What are the two protein filaments myofibrils consist of?
- Actin - thinner filament
- Myosin - thicker filament
Why do myofibrils have a striped appearance?
Light and dark bands - the light I bands are where it is just actin and no overlap, and dark A-bands of just myosin present
What is a Z line?
Line at the centre of each light band
What is a sacromere?
Distance between adjacent z-lines
What is a H zone?
Where only myosin is present so it is slightly lighter than the areas where both overlap in the dark bands of myofibrils
Describe the structure of myosin?
Globular heads which are hinged
Head has binding site for ATP and actin
Lots of myosin tails form the filament
What binding sites are present on actin?
Actin-myosin binding sites
What proteins block the actin-myosin binding sites on actin?
TROPOMYOSIN is held in place by TROPONIN
What bonds are formed when a muscle contracts?
Actin-myosin cross bridges
What triggers a muscle contraction?
When action potential arrives at a neuromuscular junction
What is a neuromuscular junction?
Point where a motor-neurone joins the muscle fibre
What is a motor unit?
All of the muscle fibres supplied by a single motor neurone
When the action potential reaches the sarcoplasmic reticulum what is stimulated?
Release of calcium ions into sarcoplasm
What do calcium ions do to allow muscles contraction to occur?
Bind to TROPONIN causing it to change shape and move TROPOMYOSIN away from binding sites on actin allowing actin-myosin bridges to form
What happens to ADP once actin is bound to myosin?
ADP detaches and ATP molecule binds causing the actin and myosin to detach
What enzyme do calcium ions activate?
ATPase, which hydrolyses ATP to ADP + Pi which releases energy
What are the 3 main sources of ATP in muscle contraction?
Aerobic respiration
Anaerobic respiration
Creating phosphate
What is creating phosphate?
Supply of phosphate readily available for ADP to bind to to make ATP
Describe the sliding filament model?
Myosin pulls actin towards the centre of the sarcomere, causing the light bands to become narrower, z lines come close together and H zone becomes narrower
How does myosin pull actin across the filament?
It’s heads which have the binding site will change angle on its hinges
What does Myosin use to return its globular head to its original position?
ATP
