Overview of the Neurological Exam

• The neurological exam is a clinical assessment tool used to determine what specific parts of the CNS are affected by damage or disease.

• The first of these is the mental status exam, which assesses the higher cognitive functions such as memory, orientation, and language.

• Then there is the cranial nerve exam, which tests the function of the 12 cranial nerves and, therefore, the central and peripheral structures associated with them.

• The gait exam, which is often considered a sixth major exam, specifically assesses the motor function of walking and can be considered part of the coordination exam because walking is a coordinated movement.

Neuroanatomy and the Neurological Exam

• Localization of function is the concept that circumscribed locations are responsible for specific functions.

Causes of Neurological Deficits

• The loss of blood flow to part of the brain is known as a stroke, or a cerebrovascular accident (CVA).

• An ischemic stroke is the loss of blood flow to an area because vessels are blocked or narrowed.

• A related type of CVA is known as a transient ischemic attack (TIA), which is similar to a stroke although it does not last as long.

• A hemorrhagic stroke is bleeding into the brain because of a damaged blood vessel.

• As blood pools in the nervous tissue and the vasculature is damaged, the blood-brain barrier can break down and allow additional fluid to accumulate in the region, which is known as edema.

Functions of the Cerebral Cortex

• The cerebral cortex is the thin layer of gray matter on the outside of the cerebrum.

The German neurologist and histologist Korbinian Brodmann, who made a careful study of the cytoarchitecture of the cerebrum around the turn of the nineteenth century, described approximately 50 regions of the cortex that differed enough from each other to be considered separate areas

Orientation and Memory

• In 1953, a bilateral lobectomy was performed that alleviated the epilepsy but resulted in the inability for HM to form new memories—a condition called anterograde amnesia.

• HM was able to recall most events from before his surgery, although there was a partial loss of earlier memories, which is referred to as retrograde amnesia.

• What he was unable to do was form new memories of what happened to him, what are now called episodic memory.

• Episodic memory is autobiographical in nature, such as remembering riding a bicycle as a child around the neighborhood, as opposed to the procedural memory of how to ride a bike.

Language and Speech

• Language is, arguably, a very human aspect of neurological function.

• Adjacent to the auditory association cortex, at the end of the lateral sulcus just anterior to the visual cortex, is Wernicke’s area.

• Both regions were originally described on the basis of losses of speech and language, which is called aphasia.

• The aphasia associated with Broca’s area is known as an expressive aphasia, which means that speech production is compromised.

• Grammar can also appear to be lost.

• The aphasia associated with Wernicke’s area is known as a receptive aphasia, which is not a loss of speech production, but a loss of understanding of content.

• Conduction aphasia associated with damage to this connection refers to the problem of connecting the understanding of language to the production of speech.

Sensorium

• The first is praxis, a practical exercise in which the patient performs a task completely on the basis of verbal description without any demonstration from the examiner.

• The second subtest for sensory perception is gnosis, which involves two tasks.

• The first task, known as stereognosis, involves the naming of objects strictly on the basis of the somatosensory information that comes from manipulating them.

• The second task, graphesthesia, is to recognize numbers or letters written on the palm of the hand with a dull pointer, such as a pen cap.

The Cranial Nerve Exam

• The twelve cranial nerves are typically covered in introductory anatomy courses, and memorizing their names is facilitated by numerous mnemonics developed by students over the years of this practice.

• The cranial nerve exam allows directed tests of forebrain and brain stem structures.

• Three of the nerves are strictly responsible for special senses whereas four others contain fibers for special and general senses.

Sensory Nerves

• Testing smell is straightforward, as common smells are presented to one nostril at a time.

• Loss of the sense of smell is called anosmia and can be lost following blunt trauma to the head or through aging.

• The Snellen chart demonstrates visual acuity by presenting standard Roman letters in a variety of sizes.

• The Rinne test involves using a tuning fork to distinguish between conductive hearing and sensorineural hearing.

• The Weber test also uses a tuning fork to differentiate between conductive versus sensorineural hearing loss.

Gaze Control

• The trochlear nerve controls the superior oblique muscle to rotate the eye along its axis in the orbit medially, which is called intorsion, and is a component of focusing the eyes on an object close to the face.

• The paramedian pontine reticular formation (PPRF) will initiate a rapid eye movement, or saccade, to bring the eyes to bear on a visual stimulus quickly.

• These areas are connected to the oculomotor, trochlear, and abducens nuclei by the medial longitudinal fasciculus (MLF) that runs through the majority of the brain stem.

• The MLF allows for conjugate gaze, or the movement of the eyes in the same direction, during horizontal movements that require the lateral and medial rectus muscles.

• The examiner is watching for conjugate movements representing proper function of the related nuclei and the MLF.

• Failure of one eye to abduct while the other adducts in a horizontal movement is referred to as internuclear ophthalmoplegia.

• Diplopia is not restricted to failure of the lateral rectus, because any of the extraocular muscles may fail to move one eye in perfect conjugation with the other.

• When the two eyes move to look at something closer to the face, they both adduct, which is referred to as convergence.

• The change in focal power of the eye is referred to as accommodation.

• Coordination of the skeletal muscles for convergence and coordination of the smooth muscles of the ciliary body for accommodation are referred to as the accommodation–convergence reflex.

• The vestibulo-ocular reflex (VOR) coordinates all of the components, both sensory and motor, that make this possible.

Nerves of the Face and Oral Cavity

• An iconic part of a doctor’s visit is the inspection of the oral cavity and pharynx, suggested by the directive to “open your mouth and say ‘ah.’

  • This is followed by inspection, with the aid of a tongue depressor, of the back of the mouth, or the opening of the oral cavity into the pharynx known as the fauces.

• The extrinsic muscles of the tongue are connected to other structures, whereas the intrinsic muscles of the tongue are completely contained within the lingual tissues.

Motor Nerves of the Neck

• The accessory nerve, also referred to as the spinal accessory nerve, innervates the sternocleidomastoid and trapezius muscles.

• The trapezius can act as an antagonist, causing extension and hyperextension of the neck.

• Lateral flexion of the neck toward the shoulder tests both at the same time.

The Cranial Nerve Exam

• The cranial nerves can be separated into four major groups associated with the subtests of the cranial nerve exam.

• First are the sensory nerves, then the nerves that control eye movement, the nerves of the oral cavity and superior pharynx, and the nerve that controls movements of the neck.

Sensory Modalities and Location

• Somatic senses are incorporated mostly into the skin, muscles, or tendons, whereas the visceral senses come from nervous tissue incorporated into the majority of organs such as the heart or stomach.

• The sensory exam tests the somatic senses, meaning those that are consciously perceived.

• Mistaking painful stimuli for light touch, or vice versa, may point to errors in ascending projections, such as in a hemisection of the spinal cord that might come from a motor vehicle accident.

• A final subtest of sensory perception that concentrates on the sense of proprioception is known as the Romberg test.

• This test can indicate deficits in dorsal column pathway proprioception, as well as problems with proprioceptive projections to the cerebellum through the spinocerebellar tract.

Muscle Strength and Voluntary Movement

• The skeletomotor system is largely based on the simple, two-cell projection from the precentral gyrus of the frontal lobe to the skeletal muscles.

• The motor exam tests the function of these neurons and the muscles they control.

• The lack of muscle tone, known as hypotonicity or flaccidity, may indicate that the LMN is not conducting action potentials that will keep a basal level of acetylcholine in the neuromuscular junction.

• A sign of UMN lesion is a negative result in the subtest for pronator drift.

Reflexes

• Reflexes combine the spinal sensory and motor components with a sensory input that directly generates a motor response.

• A deep tendon reflex is commonly known as a stretch reflex, and is elicited by a strong tap to a tendon, such as in the knee-jerk reflex.

• A superficial reflex is elicited through gentle stimulation of the skin and causes contraction of the associated muscles.

• The most common superficial reflex in the neurological exam is the plantar reflex that tests for the Babinski sign on the basis of the extension or flexion of the toes at the plantar surface of the foot.

Comparison of Upper and Lower Motor Neuron Damage

• Signs that suggest a UMN lesion include muscle weakness, strong deep tendon reflexes, decreased control of movement or slowness, pronator drift, a positive Babinski sign, spasticity, and the clasp-knife response.

• Spasticity is an excess contraction in resistance to stretch. It can result in hyperflexia, which is when joints are overly flexed.

• A lesion on the LMN would result in paralysis, or at least partial loss of voluntary muscle control, which is known as paresis.

Location and Connections of the Cerebellum

• These fibers make up the middle cerebellar peduncle (MCP) and are the major physical connection of the cerebellum to the brain stem.

• The superior cerebellar peduncle (SCP) is the connection of the cerebellum to the midbrain and forebrain.

• The inferior cerebellar peduncle (ICP) is the connection to the medulla.

• The MCP is part of the cortico-ponto-cerebellar pathway that connects the cerebral cortex with the cerebellum and preferentially targets the lateral regions of the cerebellum.

• The flocculonodular lobe is referred to as the vestibulocerebellum because of the vestibular projection into that region.

• The lateral cerebellum is referred to as the cerebrocerebellum, reflecting the significant input from the cerebral cortex through the cortico-ponto-cerebellar pathway.

Coordination and Alternating Movement

• The check reflex depends on cerebellar input to keep increased contraction from continuing after the removal of resistance.

• Testing for cerebellar function is the basis of the coordination exam.

Posture and Gait

• Gait can either be considered a separate part of the neurological exam or a subtest of the coordination exam that addresses walking and balance.

• A subtest called station begins with the patient standing in a normal position to check for the placement of the feet and balance.

Ataxia

• A movement disorder of the cerebellum is referred to as ataxia. It presents as a loss of coordination in voluntary movements.

• Ataxia is often the result of exposure to exogenous substances, focal lesions, or a genetic disorder.