ANATOMY 2MARKS-PART 7

THE CENTRAL NERVOUS SYSTEM:

  • The central nervous system consists of the brain and spinal cord. The brain plays a central role in the control of most bodily functions, including awareness, movements, sensations, thoughts, speech, and memory. Some reflex movements can occur via spinal cord pathways without the participation of brain structures.
  • The spinal cord is connected to a section of the brain called the brainstem and runs through the spinal canal. Cranial nerves exit the brainstem.
  • Nerve roots exit the spinal cord to both sides of the body.
  • The spinal cord carries signals (messages) back and forth between the brain and the peripheral nerves.

PERIPHERAL NERVOUS SYSTEM:

  • The portion of the nervous system that is outside the brain and spinal cord. The peripheral nervous system (PNS) provides the connection between internal or external stimuli and the central nervous system to allow the body to respond to its environment.
  • The PNS can be broken down into two systems.
  • The autonomic nervous system, which regulates involuntary actions such as breathing and digestion.
  • The somatic nervous system, which governs voluntary action and body reflexes.
  • The autonomic nervous system has two complementary parts.

  • The sympathetic nervous system, which activates the “fight-or-flight-or-freeze” stress response.
  • The parasympathetic nervous system, which reacts with the “rest-and-digest” response after stress.
  • The somatic nervous system coordinates voluntary physical action. It is also responsible for our reflexes, which do not require brain input.


THE CEREBRAL CORTEX:

  • The cerebral cortex is the outer covering of gray matter over the hemispheres. This is typically 2- 3 mm thick, covering the gyri and sulci.
  • The cortex (thin layer of tissue) is gray because nerves in this area lack the insulation that makes most other parts of the brain appear to be white.
  • The cortex covers the outer portion (1.5mm to 5mm) of the cerebrum and cerebellum.

FOUR CEREBRAL CORTEX LOBES:

  • Parietal Lobes
  • Frontal Lobes
  • Occipital Lobes
  • Temporal Lobes.


UPPER MOTOR NEURONS (UMN):

  • All the neurons contributing to the pyramidal and extrapyramidal systems should be called upper motor neurons (UMN).

Signs of Upper Motor Neuron Lesions (UMNL):

  • Paralysis or weakness of movements of the affected side but gross movements may be produced.
  • Superficial abdominal reflexes and cremasteric reflex are absent.
  • Spasticity or hypertonicity of the muscles.
  • Exaggerated deep tendon reflexes and clonus may be present.

LOWER MOTOR NEURONS (LMN):

The anterior horn cells and the related neurons in the motor nuclei of some cranial nerves are called lower motor neurons (LMN). Axons of these cells give rise to the peripheral motor nerves.

Signs of Lower Motor Neuron Lesions (LMNL)

  • Flaccid paralysis of muscles supplied.
  • Atrophy of muscles supplied.
  • Loss of reflexes of muscles supplied.
  • Muscles fasciculation (contraction of a group of fibers) due to irritation of the motor neurons – seen with naked eye.
  • Muscle fibrillation (contraction of individual fibers) – detected only by EMG
  • Muscle contracture (shortening of paralyzed muscles).

CORTICOSPINAL TRACT:

Four columns of motor fibers of which two run on each side of the spinal cord and which are continuations of the pyramids of the medulla oblongata.

  •   Lateral corticospinal tract.
  •   Ventral corticospinal tract.

THE SPINOTHALAMIC TRACT :

  • The spinothalamic tract is an ascending pathway of the spinal cord . It is responsible for the transmission of pain, temperature, and crude touch to the somatosensory region of the thalamus.
  • The spinothalamic tract is also known as the ventrolateral system or anterolateral system. It is a sensory tract that transmits information from the skin to the thalamus in the brain.
  • The anterior and lateral spinothalamic tracts,The former helps localize crude touch and pressure, the latter painful or temperature sensation.

THE VESTIBULOSPINAL TRACT :

  • The vestibulospinal tract is comprised of a lateral and medial pathway. The function of these tracts is to maintain equilibratory reflexes from the input of the vestibular apparatus.
  •  They will reach the axial muscles, i.e. intercostal and back muscles, as well as the extensors of the limbs.
  • Lateral vestibulospinal tract stays ipsilateral  and is NOT bilateral.
  • This tract is a part of the somatomotor ventromedial group, so it innervates proximal and axial muscles.
  • Controls posture and balance.
  • Provides extensor tone to resist the pull of gravity.
  • The Medial vestibulospinal tract is bilateral and limited to cervical spinal cord segments.

FRONTAL LOBE:

  • The frontal lobe is larger and more developed in humans than in any other organism.
  • The frontal lobe is the part of the brain that controls important cognitive skills in humans, such as emotional expression, problem solving, memory, language, judgment, and sexual behavior.
  • The frontal lobe is at the front of the brain. The right hemisphere of the frontal lobe controls the left part of the body, and vice versa.
  • Damage to the frontal lobe can create changes in personality, limited facial expressions, and difficulty in interpreting one’s environment.

 


INTERNAL CAPSULE:

  • The internal capsule is a unique location where a large number of motor and sensory fibers travel to and from the cortex.
  • The internal capsule is one of the subcortical structures of the brain.
  • The anterior limb of the internal capsule separates the caudate nucleus and lenticular nucleus.
  • The posterior limb separates the thalamus and lenticular nucleus.

CATHERINE SHALINI RAJA
M.P.T.,MIAP.,PGDYN
CARDIO RESPIRATORY PHYSCIAL THERAPIST
FITNESS & SPORTS REHABILITATION SPECIALIST

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