chapter 13 p5

Question 1

Knee-jerk reflex:
p1

Answer 1

is a reflex commonly tested by doctors.
It is a spinal reflex - this means that the neural circuit only goes up to the spinal cord, not the brain.
When the leg is tapped just below the kneecap (patella), it stretches the patellar tendon and acts as a stimulus.
This stimulus initiates a reflex arc that causes the extensor muscle on top of the thigh to contract.

Question 2

Knee-jerk reflex:
p2

Answer 2

At the same time, a relay neurone inhibits the motor neurone of the flexor muscle, causing it to relax.
This contraction, coordinated with the relaxation of the antagonistic flexor hamstring muscle, causes the leg to kick.
After the tap of a hammer, the leg is normally extended once and comes to rest.
The absence of this reflex may indicate nervous problems and multiple oscillation of the leg may be a sign of a cerebellar disease

Question 3

Knee-jerk reflex diagram

Answer 3

Question 4

Use of the knee-jerk reflex:

Answer 4

This reflex is used by the body to help maintain posture and balance, allowing you to remain balanced with little effort or conscious thought.

Question 5

Blinking Reflex p1

Answer 5

The blinking reflex is an involuntary blinking of the eyelids.
It occurs when the cornea is stimulated, for example, by being touched.
Its purpose is to keep the cornea safe from damage due to foreign bodies such as dust or flying insects entering the eye - this type of response is known as the corneal reflex.

Question 6

Blinking Reflex p2

Answer 6

A blink reflex also occurs when sounds greater than 40-60 dB are heard, or as a result of very bright light.
Blinking as a reaction to over-bright light (to protect the lens and retina) is known as the optical reflex.
The blinking reflex is a cranial reflex - it occurs in the brain, not the spinal cord.

Question 7

Neural Pathway of Blinking Reflex:

Answer 7

• When the cornea of the eye is irritated by a foreign body, the stimulus triggers an impulse along a sensory neurone (the fifth cranial nerve).
• The impulse then passes through a relay neurone in the lower brain stem.
• Impulses are then sent along branches of the motor neurone (the seventh cranial nerve) to initiate a motor response to close the eyelids.
• The reflex initiates a consensual response - this means that both eyes are closed in response to the stimulus.
• The blinking reflex is very rapid - it occurs in around one tenth of a second.

Question 8

Clinical Significance of Blinking Reflex:

Answer 8

Doctors test for the blinking reflex when examining unconscious patients. If this reflex is present, it indicates that the lower brain stem is functioning.
This procedure is therefore used as part of an assessment to determine whether or not a patient is brain-dead - if the corneal reflex is present the person cannot be diagnosed as brain-dead.

Question 9

Blinking Reflex diagram

Answer 9

Question 10

Structure of the eye:

Answer 10

Question 11

Measuring reaction time:

Answer 11

When a person catches a falling object, at least part of this response is a reflex reaction.
Measuring the time taken to catch a falling object can therefore be used to measure a person’s reaction time.
To measure the reaction time, a suitable scale is placed onto the ruler which converts the distance dropped by the ruler into a reaction time.
One investigation which can be carried out using this approach is to measure the effect of caffeine concentration on a person’s reaction time.
When carrying out this investigation, a researcher may choose to give a placebo caffeine drink to some of the people being tested.
This is a drink labelled as a caffeine drink, but contains no caffeine.

Question 12

Survival importance by reflexes:

Answer 12

Reflexes are essential for survival as they avoid the body being harmed, or reduce the severity of any damage.
For example, the iris contracts the pupil in bright light to prevent damage to the retina.
In dim light, the reverse occurs to enable you to see as much as possible.

Question 13

How Reflexes increase your chances of survival:

Answer 13

involuntary responses:
the decision-making regions of the brain are not involved, therefore the brain is able to deal with more complex responses.
It prevents the brain from being overloaded with situations in which the response is always the same.

Not having to be learnt:
they are present at birth and therefore provide immediate protection.

Extremely fast:
the reflex arc is very short. It normally only involves one or two synapses, which are the slowest part of nervous transmission.

Many reflexes are what we would consider everyday actions, such as those which keep us upright (and thus not falling over), and those which control digestion.

Question 14

three types of muscle in the body:

Answer 14

Skeletal muscle:
Cardiac muscle:
smooth muscle (Involuntary muscle):

Question 15

Skeletal muscle:

Answer 15

skeletal muscles make up the bulk of body muscle tissue.
These are the cells responsible for movement, for example, the biceps and triceps.

Question 16

Cardiac muscle:

Answer 16

cardiac muscle cells are found only in the heart.
These cells are myogenic, meaning they contract without the need for a nervous stimulus, causing the heart to beat in a regular rhythm.

Question 17

smooth muscle (Involuntary muscle):

Answer 17

involuntary muscle cells are found in many parts of the body - for example, in the walls of hollow organs such as the stomach and bladder.
They are also found in the walls of the blood vessels and the digestive tract, where through peristalsis they move food along the gut.

Question 18

differences between three types of muscle in the body:

Answer 18

Question 19

diagram of three types of muscle in the body:

Answer 19

Question 20

Structure of Muscle Fibres:

Answer 20

• Skeletal muscles are made up of bundles of muscle fibres.
• These are enclosed within a plasma membrane known as the sarcolemma.
• The muscle fibres contain a number of nuclei and are much longer than normal cells, as they are formed as a result of many individual embryonic muscle cells fusing together.
• This makes the muscle stronger, as the junction between adjacent cells would act as a point of weakness.
• The shared cytoplasm within a muscle fibre is known as sarcoplasm.

Question 21

Electrical Impulse Transmission in Muscle fibres:

Answer 21

Parts of the sarcolemma fold inwards (known as transverse or T tubules) to help spread electrical impulses throughout the sarcoplasm.
This ensures that the whole of the fibre receives the impulse to contract al the same time.

Question 22

Muscle Contraction Essentials:

Answer 22

Muscle fibres have lots of mitochondria to provide the ATP that is needed for muscle contraction.
They also have a modified version of the endoplasmic reticulum, known as the sarcoplasmic reticulum.
This extends throughout the muscle fibre and contains calcium ions required for muscle contraction.

Question 23

diagram of Muscle fibres:

Answer 23

Question 24

Myofibrils:

Answer 24

Each muscle fibre contains many myofibrils.
These are long cylindrical organelles made of protein and specialised for contraction.
On their own they provide almost no force but collectively they are very powerful.
Myofibrils are lined up in parallel to provide maximum force when they all contract together.
Myofibrils have alternating light and dark bands - these result in their striped appearance

Question 25

two types of protein filament that make up myofibrils:

Answer 25

Actin - the thinner filament.
It consists of two strands twisted around each other.

Myosin - the thicker filament.
It consists of long rod-shaped fibres with bulbous heads that project to one side.

Question 26

Myofibrils bands:

Answer 26

Light bands -
Dark bands
Z-line
H-zone

Question 27

Light bands

Answer 27

these areas appear light as they are the region where the actin and myosin filaments do not overlap.
(They are also known as isotopic bands or I-bands.)

Question 28

Dark bands

Answer 28

these areas appear dark because of the presence of thick myosin filaments.
The edges are particularly dark as the myosin is overlapped with actin
(They are also known as anisotropic bands or A-bands.)

Question 29

Z-line

Answer 29

this is a line found at the centre of each light band.
The distance between adjacent Z-lines is called a sarcomere.
The sarcomere is the functional unit of the myofibril.
When a muscle contracts the sarcomere shortens.

Question 30

H-zone

Answer 30

this is a lighter coloured region found in the centre of each dark band.
Only myosin filaments are present at this point.
When the muscle contracts the H-zone decreases.

Question 31

tnrasverse section though myofibril

Answer 31

Question 32

diagram of myofibril

Answer 32

Question 33

Drawing a labelled diagram of a sarcomere:
Key points to remember when drawing and labelling a sarcomere are:

Answer 33

Show two Z-lines to demonstrate your understanding of the length of a sarcomere.
Ensure there are heads present on the myosin filaments.
Connect actin filaments to the Z-line.
Clearly label the light and dark bands.
Show the position of the H-zone.
know the position of the A band, I band, H zone, and Z-line but do not need to learn them.

Question 34

skeletal muscle diagam

Answer 34

Question 35

diagram of sarcomere

Answer 35

Question 36

Histology of skeletal muscle:
- need to be able to identify:

Answer 36

Individual muscle fibres - long and thin multinucleated fibres that are crossed with a regular pattern of fine red and white lines.
The highly structured arrangement of sarcomeres which appear as dark (A-bands) and light (I-bands) bands.
Streaks of connective and adipose tissue.
Capillaries running in between the fibres.

Question 37

skeletal muscle diagram

Answer 37