Category Archives: Neurology (brain, spinal cord and nerves)

– Piriformis syndrome
– Sciatica

Human Brain Anatomy

Below is a narrated animation of brain anatomy. Click here to license this video on Alila Medical Media website.

The human brain is divided into three major parts :
– The cerebrum  – the largest part of human brain. The cerebrum enables sensory perception and controls voluntary motor actions.
– The cerebellum  – the cerebellum lies inferior to the cerebrum at the back of the head. It is mostly involved in coordination of movement and fine tuning of motor activities.
– The brainstem – the brainstem is located at the base of the brain and is continuous to the spinal cord. The major components of the brainstem, from rostral to caudal, are : midbrain, pons and medulla oblongata. The brainstem houses all nerve connections between different parts of the central nervous system. It provides innervation to the head and neck via cranial nerves. It also contains nuclei associated with important body functions such as regulation of blood pressure, respiration, swallowing, bladder control, sleep cycle, … among others.
Human brain anatomy labeled.
Fig. 1: Median section of human brain. Click on image to see it on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

 

On top of the brainstem, and sometimes classified as part of it, is the diencephalon. The main components of the diencephalon are:
– The thalamus – the thalamus serves as a gateway relaying sensory signals originated throughout the body to the cerebral cortex. It is also involved in emotional and memory functions.
– The hypothalamus – the hypothalamus is the major control center of the autonomic nervous system and plays essential role in homeostatic regulation. The hypothalamus links the nervous system to the endocrine system via the pituitary gland. It also contains nuclei involved in regulation of body temperature, food and water intake, sleep and wake cycle, memory and emotional behavior.
The cerebrum consists of two cerebral hemispheres. The left hemisphere controls the right half of the body. The right hemisphere controls the left half of the body. The two hemispheres are separated by a deep groove called the longitudinal fissure. Each hemisphere has a number of folds called gyri separated by grooves called sulci. A major landmark is the central sulcus.
The cerebrum has four major lobes. The frontal lobe is situated anterior to the central sulcus. It is associated mainly with voluntary motor functions, planning, motivation, emotion and social judgment.
Posterior to the central sulcus is the parietal lobe. This lobe is mainly concerned with sensory functions of the somatosensory category such as touch, stretch, movement, temperature and pain.
The temporal lobe is separated from the frontal and parietal lobes by the lateral sulcus. The temporal lobe is associated with hearing, learning, visual memory and language.
The occipital lobe is located at the rear of the cerebrum. This is the visual processing center of the brain.

Lobes of the brain
Fig. 2: Lobes of the brain. Click on image to see it on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

 

 

At first glance, the two hemispheres look identical, but research has found a number of differences between them. This is called lateralization of brain function. For example, the language formation areas – the Wernicke’s and Broca’s areas – are usually located in the left hemisphere of right-handed people. Lesions to these areas result in language comprehension deficits or speech disorders. The corresponding areas in the right hemisphere are responsible for emotional aspect of language. Lesions to these areas do not affect speech comprehension and formation, but result in emotionless speech and inability to understand the emotion behind the speech such as sarcasm or a joke.

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Sciatica

The videos on this page can be downloaded upon purchase of a license on Alila Medical Media website. Click here!


Sciatica  or sciatic neuralgia is a common condition in which one of the spinal nerve roots of the sciatic nerve is compressed resulting in lower back, buttock and leg pain. Sciatic nerve is a large nerve derived from 5 spinal nerve roots (L4, L5, S1, S2 and S3). It runs from the lumbar spine through the buttock down the leg and foot on the posterior side. There is one sciatic nerve on each (right and left) side of the body. Typically only one side of the body is affected.

Sciatica
Fig. 1 : Sciatic nerve anatomy and pain patterns of sciatica. Only one side (right leg) is illustrated for simplicity. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

Symptoms

A typical sciatica pain is described as a sharp shooting pain in the lower back, down the buttock, thigh and leg on one side of the body. There may also be numbness, burning and tingling sensations. The pain can get worse with sitting, moving, sneezing, or coughing.

The patterns of pain depend on which nerve root is compressed, and follow the dermatome distribution (Fig. 1).

Causes

The most common cause of sciatica is herniated spinal disc. The spinal disc is a soft elastic cushion that sits in between the vertebrae of the spine. With age, the discs become rigid and may crack, the gel-like center of the disc may protrude out and become a herniation outside the normal boundaries of the disc. Disc herniation presses on the nerve root as it exits the spine.
Lumbar spine labeled diagram.
Fig. 2 : Anatomy of the lumbar spine, lateral view. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

Lumbar disc herniated.
Fig. 3 : Normal disc and herniated disc, superior view. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

Treatment

In majority of the cases the condition resolves by itself after a few weeks of rest and conservative treatment. Pain relief, nonsteroidal anti-inflammatory drugs and muscle relaxants may be prescribed. Stretching exercises and physical therapy may be recommended.

Surgery may be needed if the the pain doesn’t go away after 3 months or more of conservative treatments. The herniated disc may be removed (discectomy) or part of the bone of the vertebrae may be cut to make room for the nerve (laminotomy).

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Piriformis syndrome


Piriformis syndrome (PS) is a neuromuscular condition where the piriformis muscle – one of the deep gluteal muscles – presses on and compresses the sciatic nerve causing pain, tingling and numbness in the buttock area, and down the path of sciatic nerve to the thigh and leg. Sciatic nerve runs under the piriformis muscle (Fig. 1) and may be irritated when the muscle is too tight or shortened due to spasms. Piriformis syndrome is to be differentiated from sciatica which shows similar symptoms but has different causes.

Piriformis syndrome

Fig. 1 : Piriformis syndrome. Posterior view of the pelvis showing location of piriformis muscle and sciatic nerve. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

 

 

 

 

Diagnosis is difficult as it produces similar symptoms as sciatica and is commonly done by exclusion of sciatica caused by compression of sciatic nerve roots by a herniated disc.

Lumbar spine disc herniation.
Fig. 2 : Sciatica caused by compression of spinal nerve roots by a herniated disc. Lateral view of the lumbar spine. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.  

 

 

 

 

Causes and Risk factors

–  Anatomical abnormality of the nerve/muscle relation. Some people are more likely to get PS than others.

– Tightness or spasm of piriformis muscle due to overuse injury. This commonly happens in sport activities that put pressure on the piriformis muscle such as bicycling, running without proper stretching, or any activity that involves repeated movements of the leg performed in sitting position.

Treatment

– Conservative treatment includes stretching exercises, massage, avoidance of causative activities.

– Physical therapy that strengthens the gluteus maximus, gluteus medius, and biceps femoris is usually recommended to reduce strain on the piriformis muscle.

– Relief of symptoms may be achieved with anti-inflammatory drugs or muscle relaxants.


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