Primitive reflexes

These are present in normal neonates and young infants but

disappear as the nervous system matures (p. 305). People

with congenital or hereditary cerebral lesions and a few healthy

individuals retain these reflexes, but their return after early

childhood is often associated with brain damage or degeneration.

Although often referred to as frontal, the primitive reflexes (snout,

grasp, palmomental and glabellar tap) have little localising value

and in isolation are of little significance, but in combination suggest

diffuse or frontal cerebral damage (Box 7.10). Unilateral grasp and

palmomental reflexes may occur with contralateral frontal lobe

pathology. The glabellar tap is an unreliable sign of Parkinson’s

disease.

Coordination

Performing complex movements smoothly and efficiently depends

on intact sensory and motor function and an intact cerebellum.

Anatomy

The cerebellum lies in the posterior fossa and consists of two

hemispheres with a central vermis. Afferent and efferent pathways

convey information to and from the cerebral motor cortex, basal

ganglia, thalamus, vestibular and other brainstem nuclei and the

spinal cord. In general, midline structures, such as the vermis,

7.10 Primitive reflexes

Snout reflex

• Lightly tap the lips. Lip pouting is an abnormal response

Grasp reflex

• Firmly stroke the palm from the radial side. In an abnormal

response, your finger is gripped by the patient’s hand

Palmomental reflex

• Apply firm pressure to the palm next to the thenar eminence with a

tongue depressor. An abnormal response is ipsilateral puckering of

the chin

Glabellar tap

• Stand behind the patient and tap repeatedly between their eyebrows

with the tip of your index finger. Normally, the blink response stops

after three or four taps

142 • The nervous system

Examination sequence

• Ask the patient to perform an imaginary act, such as

drinking a cup of tea, combing their hair, or folding a letter

and placing it in an envelope.

• Ask the patient to copy movements you make with your

fingers, such as pointing or making a V sign.

• Ask the patient to copy a geometric figure (interlocking

pentagons or cube).

• Ask the patient to put on a pyjama top or dressing gown,

one sleeve of which has been pulled inside out.

• Ask the patient to lie on the couch and perform cycling

movements with their legs.

The patient may be unable to initiate a task or may perform

it in an odd or bizarre fashion. Constructional apraxia (difficulty

drawing a figure) is a feature of parietal disturbance. Dressing

apraxia, often associated with spatial disorientation and neglect,

is usually due to parietal lesions of the non-dominant hemisphere.

Patients with gait apraxia have difficulty walking but are able to

perform cycling movements on the bed surprisingly well.

Sensory system

The sensory system comprises the simple sensations of light

touch, pain, temperature and vibration, together with joint position

sense (proprioception) and higher cortical sensations, which

include two-point discrimination, stereognosis (tactile recognition),

graphaesthesia (identification of letters or numbers traced on

the skin) and localisation.

Detailed examination of sensation is time-consuming and

unnecessary unless the patient volunteers sensory symptoms

or you suspect a specific pathology, such as spinal cord

compression or mononeuropathy. In patients without sensory

symptoms, assessing light touch of all four limbs as a screening

process may suffice. It is useful to have a working knowledge

of the dermatomal distribution (a dermatome is an area of skin

innervated by a single nerve root) and sensory distribution of

the more commonly entrapped peripheral nerves (see Figs 7.26

and 7.27 later).

Anatomy

Proprioception and vibration are conveyed in large, myelinated

fast-conducting fibres in the peripheral nerves and in the posterior

In more severe cases there may be a tremor (or an increase in

amplitude of tremor) of the finger as it approaches the target finger

and the patient’s own nose (intention or hunting tremor). The

movement may be slow, disjointed and clumsy (dyssynergia). The

heel-to-shin test is the equivalent test for the legs. It is abnormal

if the heel wavers away from the line of the shin. Weakness may

produce false-positive finger-to-nose or heel-to-shin tests, so

demonstrate that power is normal first.

Dysdiadochokinesis (impairment of rapid alternating movements)

is evident as slowness, disorganisation and irregularity of

movement. Dysarthria and nystagmus also occur with cerebellar

disease. Much less reliable signs of cerebellar disease include

the rebound phenomenon (when the displaced outstretched

arm may fly up past the original position), pendular reflexes

and hypotonia.

In disorders predominantly affecting midline cerebellar

structures, such as tumours of the vermis and alcoholic cerebellar

damage, the tests described may be normal and truncal ataxia

(that is, ataxic gait) may be the only finding. In the most severe

cases this may mean that the patient cannot sit unsupported.

Cerebellar dysfunction occurs in many conditions, and the

differential diagnosis varies with age and speed of presentation.

Apraxia

Apraxia, or dyspraxia, is difficulty or inability to perform a task,

despite no sensory or motor abnormalities. It is a sign of higher

cortical dysfunction, usually localising to the non-dominant frontal

or parietal lobes.

Fig. 7.23 Performing the heel-to-shin test with the right leg.

A

1

1

2

2

B

Fig. 7.22 Finger-to-nose test. A Ask the patient to touch the tip of their nose (1) and then your finger (2). B Move your finger from one position to

another, towards and away from the patient (1), as well as from side to side (2).

Sensory system • 143

7

the patient means lack of sensation rather than weakness or

clumsiness. Neuropathic pain (pain due to disease or dysfunction

of the PNS or CNS) is often severe and refractory to simple

analgesia. Reduced ability to feel pain may be accompanied by

scars from injuries or burns (trophic injuries). Sensory symptoms

are defined as follows:

• paraesthesia: tingling, or pins and needles

• dysaesthesia: unpleasant paraesthesia

• hypoaesthesia: reduced sensation to a normal stimulus

• analgesia: numbness or loss of sensation

• hyperaesthesia: increased sensitivity to a stimulus

• allodynia: painful sensation resulting from a non-painful

stimulus

• hyperalgesia: increased sensitivity to a painful stimulus.

Examination sequence

The aim here is to focus the examination. Look for a sensory

level if the history and examination suggest spinal cord

pathology; a glove and stocking pattern usually starting

distally, caused by a peripheral neuropathy; or sensory

disturbance in a specific nerve territory or dermatome. Be

guided by the history and the examination findings from the

motor system and reflexes. It is useful to ask the patient to

map out their area(s) of sensory disturbance if they can.

Light touch

• While the patient looks away or closes their eyes,