When a muscle is activated, it shortens and, in doing so, it exerts a force on the tendons to which it is attached. List the five items that the amount of force exerted by the muscle depends on [5 marks]
- NUMBER OF FIBRES CONTRACTING CAN VARY:
- each muscle fibre is innervated by only one axon, but each axon branches and innervates several muscle fibres
- a motor unit consists of one motor neuron and all muscle fibres it innervates, so all muscle fibres in a motor unit contract simultaneously
- the strength of contraction is graded by varying the number of active motor units
- each muscle fibre is innervated by only one axon, but each axon branches and innervates several muscle fibres
- CROSS-SECTIONAL AREA OF MUSCLE:
- there will be more myofibrils in parallel which increases per cell rather than increased cell numbers due to physical training - FREQUENCY OF STIMULATION:
- a series of action potentials, when sufficiently closely spaced, produces summation of tension (tetanus)
- tetanic tension depends on action potential frequency, increasing with this frequency
- a fused tetanus shows no ripple of tension corresponding to action potential frequency - RATE AT WHICH MUSCLE SHORTENS:
- determined by the force velocity curve - ISOMETRIC TENSION (FORCE):
- depends on muscle length
- declines at lengths longer or shorter than an optimum length for that muscle
Name FIVE functions of the respiratory system? [5 marks]
- Pulmonary ventilation
- Exchange of gases between the blood and lungs
- Exchange of gases between the blood and the tissues
- Sound created by air vibrating the vocal cords
- Olfaction
Which chemoreceptors control the rate and depth of respiration in humans and where in the body are they situated? [4 marks]
- A rise in plasma CO2 leads to increased CO2 uptake into the brain, where it is converted into bicarbonate and hydrogen ions via carbonic acid
- The hydrogen ions stimulate the central chemoreceptors and this increases the rate and depth of respiration
- A fall in plasma CO2 has the opposite fact, i.e. more carbonic acid and thus less hydrogen ions, so decreases the rate and depth of respiration
- They are located on the ventrolateral medullary surface in the vicinity of the exits of cranial nerves IX and X
How is oxygen carried in the blood? What factors determine the oxygen content of a given sample of blood? [4 marks]
- Oxygen is carried bound to haemoglobin (an oxygen-binding protein) in red blood cells
- At the centre of each of four haem groups that make up haemoglobin s a ferrous iron that can loosely bind one molecule of oxygen
- Therefore, each haemoglobin can carry four oxygen molecules
4+5. The affinity of haemoglobin for oxygen is determined by:
- pH
- partial pressure of CO2
- concentration of 2,3-biphosphoglycerate
Define the term hematocrit and give an approximate value for an individual normally
living at sea level. If such a person were to live for a period of months at high altitude,
what would happen to their hematocrit (assuming no genetic adaptation)? [3 marks]
- DEFINITION: the ratio of the volume of red blood cells to the total volume of blood; i.e. the proportion of the total volume of blood occupied by red blood cells.
- An average value at sea level is about 0.47 litres per whole litre of blood.
- After two months at high altitude, the individual’s hematocrit value would INCREASE
Define the terms preload and afterload as applied to the heart [4 marks]
PRELOAD:
the end-diastolic volume (EDV) at the beginning of systole and is directly related to the degree of stretch of the myocardial sarcomeres (basis of the Frank-Starling Law of the Heart)
AFTERLOAD:
the ventricular pressure at the end of systole (ESP); ejection stops because the ventricular pressure developed by the myocardial contraction is less than the arterial pressure; this determines the end-systolic volume (ESV)
STROKE VOLUME = EDV - ESV
CARDIAC OUTPUT = STROKE VOLUME x HEART RATE
Name the hormones released from the posterior pituitary gland. What are their principal actions? [4 marks]
VASOPRESSIN: targets the KIDNEY
1. increases the permeability of the collecting ducts to water
OXYTOCIN: targets the BREASTS + ADRENAL MEDULLA
- stimulates the ejection of milk from the mammary glands in response to suckling
- may also play a role in expelling the foetus and placenta during labour
- in males, it is believed to play a role in erection, ejaculation, and sperm progression
Define what is meant by osmotic pressure and osmosis [4 marks]
1+2. Osmosis is the movement of water from an area of high water potential to an area of low water potential through a partially permeable membrane
3+4. Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
Give an example of simple diffusion and facilitated diffusion [2 marks]
- Simple diffusion:
the diffusion of oxygen molecules to the blood stream from the alveoli - Facilitated diffusion:
transport of glucose across the basolateral membrane of the cells of the small intestine using the GLUT2 carrier proteins
What is a motor unit? [2 marks]
A motor unit is made up of a) a motor neuron and b) all the skeletal muscles innervated by its axon terminals
What are the two main spinal tracts that transmit information from the periphery to the sensory cortex? [2 marks]
SPINOTHALAMIC TRACT
and
SPINCEREBELLAR TRACT
What are the functions of saliva and how is its rate of secretion regulated? [3 marks]
- Lubricates food to facilitate swallowing
- Contains the enzyme salivary-alpha-amylase that begins the process of starch digestion
- Dissolves certain substances in food, making them available to taste cells
- Contains IgA and lysozyme, which act on the walls of certain bacteria causing cell lysis and death
* The rate of salivary secretion is controlled primarily by reflexes mediated by the autonomic nervous system
The pH of gastric juice is very low (pH 1-3). List FIVE reasons why HCL is important in the gastrointestinal tract [5 marks]
- Helps in the breakdown of connective tissue and muscle fibres of ingested meat
- Activates inactive pepsinogen
- Provides optimal conditions for the activity of pepsins
- By combining with calcium and iron to form soluble salts, HCL aids in the absorption of these minerals
- It acts as an important defense mechanism, killing many of the microorganisms that may cause infection (e.g. typhoid, salmonella, cholera, and dysentry)
