The Nervous System: Structure and Sensorimotor Function for PT Aides

The Nervous System: Overview for PT Aides

The nervous system controls every movement a patient makes and every sensation they report. As a PT aide, you will work daily with patients who have nervous system injuries or diseases. Understanding how the system is organized helps you follow the physical therapist's plan of care, communicate observations accurately, and keep patients safe.

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord. Three brain regions are especially important for motor control in PT practice.

Motor cortex — A strip of tissue along the top of each cerebral hemisphere that initiates voluntary movement. The left motor cortex controls the right side of the body, and the right motor cortex controls the left side. This is why a stroke in the left hemisphere typically causes right-sided weakness (hemiplegia or hemiparesis).

Basal ganglia — A group of structures deep in the brain that help smooth out and regulate voluntary movement. Damage here causes conditions such as Parkinson's disease, where patients show tremor, rigidity, and difficulty starting movement.

Cerebellum — Located at the back of the brain, the cerebellum coordinates timing and precision of movement. Cerebellar damage produces ataxia — unsteady, poorly coordinated movement.

The spinal cord runs from the brainstem down through the vertebral column and is divided into four regions by their vertebral level: cervical (C1–C8), thoracic (T1–T12), lumbar (L1–L5), and sacral (S1–S5). Segments at each level send and receive signals through nerve roots that exit between the vertebrae.

Peripheral Nervous System (PNS)

The PNS includes all nerves outside the brain and spinal cord. Nerve roots from adjacent spinal cord levels join together to form plexuses — networks that give rise to the named peripheral nerves supplying the limbs.

Brachial plexus — Formed by nerve roots C5–T1. It supplies the shoulder, arm, forearm, and hand. Common injuries include those from difficult deliveries at birth or trauma to the shoulder and neck.

Lumbosacral plexus — Formed by roots L1–S4 and supplies the hip, thigh, leg, and foot. The sciatic nerve, the body's largest peripheral nerve, arises from this plexus (L4–S3). Compression of the sciatic nerve causes the pain pattern known as sciatica.

Motor signals travel from the CNS out through motor (efferent) fibers to muscles. Sensory signals travel inward through sensory (afferent) fibers from the skin, joints, and muscles back to the spinal cord and brain.

Dermatomes

A dermatome is the area of skin supplied by a single spinal nerve root. Dermatome maps allow clinicians to match a patient's area of altered sensation to a specific spinal cord level. For example:

• Numbness along the thumb side of the forearm and thumb itself often indicates involvement of C6.
• Numbness in the little finger and the inner forearm often points to C8.
• Numbness running down the outer calf and into the big toe is associated with L4–L5.
• Numbness in the back of the thigh and heel area is associated with S1.

When a PT asks a patient "Do you feel that?" while touching an area, the PT is testing sensation to check which dermatome levels are intact. As an aide, you may be asked to report patient responses during exercises, so understanding why the PT is checking sensation helps you communicate accurately.

Common Neurological Conditions in PT

Stroke (cerebrovascular accident, CVA) — A stroke occurs when blood supply to part of the brain is disrupted, causing brain cells to die. Motor cortex damage produces contralateral (opposite-side) weakness or paralysis, increased muscle tone (spasticity), and exaggerated reflexes. Patients may also show sensory loss, speech difficulties, and balance problems. PT focuses on retraining movement, improving balance, and preventing falls and secondary complications such as contractures.

Spinal cord injury (SCI) — Damage to the spinal cord disrupts motor and sensory signals below the injury level. A complete injury means no motor or sensory function is preserved below that level. An incomplete injury means some function remains. The higher the injury level, the more of the body is affected. Cervical injuries can impair breathing and all four limbs (tetraplegia). Thoracic or lumbar injuries affect the lower body (paraplegia). PT aides must be alert to skin integrity, positioning, and the risk of pressure injuries in patients with SCI who cannot feel discomfort.

Peripheral nerve injury — Damage to a nerve outside the CNS causes weakness or paralysis and numbness in the specific muscles and skin the nerve supplies. Recovery is possible because peripheral nerves can regenerate, unlike CNS tissue. For example, injury to the radial nerve at the upper arm causes wrist drop (inability to extend the wrist). PT works to maintain joint range of motion and retrain movement as the nerve heals.

Safety Points for PT Aides

• Never progress a neurological patient's activity without the PT's instruction. Responses can be unpredictable and the risk of falls is elevated.
• Report any new or changed symptoms — sudden increase in weakness, new numbness, loss of bladder or bowel control, or severe headache — to the supervising PT immediately. These can signal a medical emergency.
• Patients with sensory loss cannot reliably report pain from pressure, heat, or a brace that fits poorly. Check skin regularly as directed and report any redness or skin breakdown.
• Maintain competency in CPR and first aid; neurological patients carry elevated risk for cardiac and respiratory events.