BMS120 Human Physiology and Anatomy Practical Handbook

Human Physiology and Anatomy Practical Handbook

Module co-ordinator: Yasser Abdel-Wahab
Name of student:
Student registration number:
Course title:Contents:
Introduction
3
A: Neuromuscular function: the reflexes
4
B: Electromyography
9
C: Vascular function: cardiovascular sounds and blood pressure &
Cardiac function: electrocardiogra
10
D: Respiratory function: respiratory movements
20
E: Renal function: urine excretion and composition
25
2Introduction
Laboratory-based practical classes form an integral part of the Human Physiology and Anatomy
module (BMS120) allowing each student the opportunity to carry out laboratory procedures
which demonstrate physiological function.
Yasser Abdel-Wahab
Module coordinator

Neuromuscular Function: The Reflexes and Chart / PowerLab Tutorial

Aims of Practical Exercises

The practical and associated exercises aim to:

• Provide a greater understanding of the neuromuscular system by performing a number of diagnostic
  reflex tests
• Give an appreciation of the importance of these techniques in clinical medicine
• Review relevant aspects of neuromuscular function through completion of a number of additional
  exercises

Background on Reflexes

Automatic stereotyped responses to various types of stimuli allow animals to adjust quickly to adverse
environmental changes. These automatic responses are generated by the nervous system and are
collectively termed reflexes.
Reflexes which result in automatic regulation of body function can either be somatic or visceral.
Somatic reflexes involve skeletal muscle responses while visceral reflexes involve adjustments of
smooth and cardiac muscle and response of glands to stimuli.
The neural pathway utilized in performing a reflex is called a reflex arc. As such, the reflex arc is the
functional unit of neural activity and human activities rely upon the operation of simple or complex
reflex arcs.

The Somatic Reflex Arc Components

The principal components of a somatic reflex arc are:

1. A receptor: a structure such as a neuromuscular spindle or cutaneous end-organ that is specialized
   to respond to the original stimulus
2. A sensory (afferent) neuron: which carries impulses through a peripheral nerve and posterior root,
   thus relaying information to the spinal cord
3. An interneuron (association neuron): which forms synaptic connections between the sensory and
   motor neuron in the gray matter of the spinal cord, relaying and processing the signal across one
   or more synapses
4. A motor (efferent) neuron: which transmits signals (nerve impulses) from the central nervous
   system through the anterior root to the effector via a peripheral nerve
5. An effector: a muscle or gland innervated by the motor neuron, responding to the stimulus by
   contracting

Reflex arcs have more than one interneuron, or may even completely lack interneurons. When a reflex
arc has no interneuron (eg. the knee jerk reflex) it is said to be monosynaptic, whereas a reflex arc with
one or more interneurons is termed polysynaptic. Some reflex arcs are single-sided (ipsilateral), that is
they only involve afferent and efferent pathways on one side of the brain and spinal cord. Others
additionally use efferent pathways on the opposite side to the incoming stimulus (contralateral reflexes).

Somatic Reflexes in Amphibian Models

Key Features of Somatic Reflexes

Somatic reflexes, whether in amphibians or humans have five key features worthy of
consideration: (a) function; (b) speed of reaction; (c) radiation; (d) inhibition; and (e) synaptic
fatigue. Classical physiology experiments used to be performed using the frog as a model.
Reflex studies were performed using a "pithed" frog (a frog with its brain destroyed but
retaining an intact spinal cord). The process of "single pithing", quickly produces a laboratory
specimen (referred to as a spinal frog), which is unable to perceive pain and is unaware of the
procedures.

Spinal Frog Preparation for Reflex Testing

The spinal frog preparation can be used to test:

1. Functional nature of reflexes: where the studies reveal that changes in muscle tone,
   movement, and coordinated action occur independently of cognition and result from
   reflex activity
2. Reaction time of reflexes: where the studies reveal that reaction time to a stimulus is
   influenced by the strength of the stimulus
3. Reflex radiation: a phenomenon observed when the foot of the spinal frog is subjected to
   increasing intensities of electrical stimulation resulting in a changes of reflex pattern
4. Reflex inhibition: where studies reveal that electrical stimulation can override a refex
   action in the leg of the spinal frog observed in response to dipping the toes in an acidic
   solution
5. Synaptic fatigue: a phenomenon observed when the sciatic nerve is overstimulated

Reflexes and Medical Diagnosis

As interruption of the reflex arc at any point abolishes the response to the stimulus, reflex
testing is a fundamental clinical procedure used by physicians searching for possible
neurological pathology. Reflex studies can prove a useful aid in assessing a number of
conditions including, damage to intervertebral disks, tumours, polyneuritis and apoplexy.
The interpretation of a reflex response is often subjective and as such requires considerable
experience. The purpose of this practical is not to diagnose but rather to test, observe and
appreciate the value of certain tests from a physiological viewpoint.

Clinical Characterization of Reflexes and Their Aberrations

Types of Clinical Reflexes

Clinically reflexes are categorized as one of two types:

1. Deep reflexes
   • Include all reflexes elicited by a sharp tap on a tendon or muscle
   • Also called jerk, stretch or myotactic reflexes
   • Receptors for these reflexes are located in muscle, not tendon
   • When tendon is tapped, muscle stretches, in turn activating the muscle spindle thus
     triggering the reflex response
2. Superficial reflexes
   • Withdrawal reflexes elicited by noxious or tactile stimulation
   • Also called cutaneous reflexes
   • Stroking or scratching the skin is a sufficient stimulus to induce a response

Abnormal Reflex Responses

Abnormal reflex responses to stimuli may be diminished (hyporeflexia), exaggerated
(hyperreflexia) or pathological.
Hyporeflexia is often due to malnutrition, neurological lesions, ageing or deliberate relaxation.
Hyperreflexia is often accompanied by marked muscle tone, due to loss of inhibitory control by the
motor cortex; this condition can be induced by strychnine poisoning.
Pathological reflexes are responses which occur in one or more muscles other than the muscle in
which the stimulus originates.
These three abnormal responses are what a physician looks for when performing these tests using the
following scale to gauge each response:
Very brisk, hyperactive; often indicative of pathology; may be associated with spasms
+++
Brisker than average, may or may not be indicative of pathology
++
Average; normal
+
Somewhat diminished
-
No response

Experimental Protocol: Somatic Reflexes in Humans

Try to elicit the following reflexes in a subject. These are a few of the reflexes commonly tested in
clinical diagnosis to obtain information regarding the function of muscles, peripheral nerves and the
CNS.

Materials for Reflex Testing

Reflex hammer
Pencil or key

1. Hoffmann's Reflex

This is a deep reflex in which the response does not occur only in the muscle that is stretched. If the
response to the stimulus is broad, that is it affects several fingers other than the finger stimulated, then
there is indication of pyramidal tract (spinal cord) damage. To elicit this reflex, flick the terminal
phalanx of the index finger upward as shown in Figure A1.
Figure A1. Method used to elicit Hoffmann's reflex
If the thumb is adducted and flexed and the other fingers exhibit twitch-like flexion, this indicates
pathology. Such a wide ranging reflex action resulting from a brief stretch of the flexor muscles of the
index finger indicates deep reflex hyperactivity and pathological characteristics.

2. The Patellar Reflex

This monosynaptic reflex is also referred to as the knee reflex, knee jerk or quadriceps reflex. The
subject should be seated on the edge of a laboratory bench with the leg suspended and somewhat flexed
over the edge.
Figure A2. Method used to elicit the patellar reflex
To elicit the typical response, strike the patellar tendon Just below the kneecap, at the posit' ion
indicated in Figure A2.
Should the response be negative, utilize the Jendrassic manouver for facilitation. This manouver
involves the subject locking the fingers of both hands in front of the body and pulling each hand against
each other isometrically.
A phenomenon called clonus is sometimes observed when inducing this reflex. Clonus is characterized
by a succession of jerklike contractions (spasms) which follow the normal response and persist for a
period of time. As such, this condition is a manifestation of hyperreflexia, indicating damage within the
central nervous system.
This reflex functions through L2, L3, and L4 spinal nerves.

3. Achilles Reflex

This reflex is often referred to as the ankle jerk. It is characterized by plantar flexion when the Achilles
tendon is dealt a sharp blow. Stretching this tendon affects the muscle spindles in the triceps surae,
causing it to contract. To elicit this response, first grip the subject's bare foot with the left hand, as
illustrated in Figure A3, forcing it upward somewhat. With the subject relaxed, strike the Achilles
tendon as shown. Hyporeflexia here is often associated with hypothyroidism.
Figure A3. Method used to elicit Achilles reflex
Test this reflex in both legs.
This reflex functions through SI and s2 spinal nerves.

4. Plantar Flexion (Babinski's Sign)

Unlike those above, this reflex tends to be of a superficial nature. As shown in Figure A7, the normal
reaction to stroking the sole of the foot (eg. with the blunt end of pencil or a key) in an adult is plantar
flexion (extension of the foot at the ankle joint) accompanied by adduction of the toes (i.e. movement
towards the axis or mid-line of the body or one of its parts). If dorsiflexion occurs, i.e. the toes abduct
(move away from the axis or ntid-line of the body or one of its parts) and dorsiflex (flexion of the foot at
the ankle joint) as shown on the right of Figure A4, it may be assumed that there is pathology.
Dorsiflexion starts in the big toe and spreads to the others (Babinski's sign), signifying damage to myelin
in the fibres of the pyramidal tracts.
Babinski's sign can occur in adults during sleep and in epileptics immediately after a seizure, but usually
indicates a lesion in the corticospinal tracts, or peripheral nerve damage. It is important to note that
dorsiflexion is considered normal in infants up to six months, particularly if they are asleep.
However, Babinski's sign disappears in infants once myelinization of nerve fibres is complete.
Figure A4. Method used to elicit plantar flexion (left) and Babinski's sign (right)
Test this reflex, following the pattern shown in the middle illustration of Figure A4, on both feet.
This reflex functions through S1, and S2 spinal nerves.