Learning Outcomes

• To describe the major components of the Central, Peripheral and Autonomic Nervous systems.

• To understand the functions of these components.

• To explain how a nervous impulse is transmitted.

• To explain the underlying physiology behind the lesions/damage that occurs in the nervous system.

Spinal cord structure

Spinal cord has two main functions:

1). SC connects a large part of the peripheral nervous system to the brain.

2) SC acts as a minor coordinating centre responsible for some simple reflexes (e.g withdrawal reflex).

31 pairs of spinal nerves arise along the spinal cord

• Extension of brain stem

• Long slender cylinder of nerve tissue (~45 cm long, 2cm diameter).

• Enclosed by a protective vertebral column (vertebrae).

• Paired spinal nerves emerge from spinal cord.

• Spinal nerves named according to region of vertebral column from which they emerge.

Peripheral Nervous System

• 31 pairs of Spinal nerves

• 12 pairs of Cranial nerves

• Autonomic Nervous System

8 pairs: Cranial Nerves

12 pairs: Thoracic Nerves

5 pairs: Lumbar Nerves

5 pairs: Sacral Nerves

1 Pair: Coccygeal Nerves

• During development, vertebral column grows ~25cm longer than SC.

• Nerves pass down SC and exit at particular points from the vertebral column.

• At the lower end of vertebral column is a thick bundle of elongated nerve roots called Cauda Equina (‘horses tail’).

At this region Spinal Taps

can be taken (collection of CSF).

No SC, so no damage caused.

• A cross section of the SC shows it is composed of grey matter in the centre surrounded by white matter.

Ventral horn

White matter

Grey matter

Dorsal horn

Grey Matter.

– resembles the letter H (butterfly)

– consists of mixture of multipolar neurone cell bodies (colour)

– consists of 2 prominent projections:

• Posterior Dorsal Horn

• Anterior Ventral Horn

Dorsal Horn:

• Groups of afferent fibres carrying impulses from peripheral sensory receptors enter through the dorsal root into here.

Ventral Horn:

• Nerve fibres exit from here through ventral roots to skeletal muscles.

Dorsal and ventral roots are very short and

fuse to form the spinal nerves.

Poliomyelitis:

polio = grey matter

myelitis = inflammation of SC

• Polio virus enters through faeces contaminated water.

• Polio virus causes destruction of anterior ventral horn motor neurones.

• Muscles atrophy due to wasting (astronauts)

• Death by paralysis of respiratory or cardiac muscle

• Salk and Sabin polio vaccines eliminated disease.

White Matter

- Composed of myelinated and unmyelinated nerve fibres.

- Divided into:

Posterior funiculi

Lateral funiculi

Anterior funiculi

Spinal Cord Segments

• Spinal tracts are bundles of axons grouped together into columns that extend length of the spinal cord

• A spinal tract consist of neuronal axons that have a similar destination and function

• Part of a multineurone pathway that connect the brain to the rest of the body

• Each tract either:- begins with a particular part of the brain (Motor / descending tract)

- ends with a particular part of the brain(Sensory /ascending tract)

• Tracts are named according to their origin and point of termination.

The Brain

• The brain is organised into several different regions dependent upon function, anatomy and development.

1). Brain stem:

- Midbrain

- Pons

- Medulla

2). Cerebellum:

3). Forebrain:

• Although specific activity is attributed to particular regions, complex interplay between regions exists.

• A majority of the brain which we recognise is the Cerebrum (outer wrinkly part).

• Deep folds divide each half of the Cerebrum into 4 major lobes.

- Occipital lobes: process visual input- Temporal lobes: process sound- Parietal lobes: receive and process somesthetic

sensations (touch, pressure, heat, cold, pain) and proprioception

(awareness of body position)- Frontal lobes: 3 functions:

voluntary motor activity, speaking ability, thought

Cerebral Hemispheres (Cerebrum).

• Largest part of the brain

• Account for about 80% of brain weight.

• Divided into 2 halves:

- Right cerebral hemisphere

- Left cerebral hemispheres.

• They are connected together by the Corpus Callosum.

• This is a thick band of neuronal axons transversing between the 2 hemispheres.

• The entire surface of the cerebral hemispheres are marked by elevated ridges of tissue called Gyri.

• These are separated by shallow grooves called sulci.

• The deepest of these grooves are called fissures.

• The median longitudinal fissure separates the cerebral hemispheres from one another.

• The transverse fissure separates the cerebral hemispheres from the cerebellum below it.

Parts of the Brain

• Cerebrum• Thalamus• Hypothalamus• Cerebellum• Midbrain• Pons• Medulla Oblongata

Cerebral lobes and their function

• Frontal: - voluntary motor activity

- speech

- thought

• Temporal: - process sound

• Occipital: - process visual input

• Parietal: - process somesthetic sensations (touch, pressure, heat, cold

- proprioception; awareness of body position

www.smc.edu

The Brain

– Cerebral cortex: cognition, senses, movement

– Cerebellum: coordination of muscle contraction

– Thalamus: relay center

– Hypothalamus: homeostasis

– Limbic System: instincts, emotions

– Brain Stem: medulla controls breathing, blood pressure, heart rate

Parts of the Brain

Cerebrum

Thalamus

Hypothalamus

Cerebellum

MidbrainPons

Medulla Oblongata Tortora, G. J. and Grabowski, S.

(2000) Principles of Anatomy and Physiology

The Cerebrum

www.smc.edu

www.smc.edu

Spinal cord has two main functions:

1). SC connects a large part of the peripheral nervous system to the brain.

2) SC acts as a minor coordinating centre responsible for some simple reflexes (e.g withdrawal reflex).

• 31 pairs of spinal nerves arise along the spinal cord

The Spinal Cord

Peripheral Nervous System

• 31 pairs of Spinal nerves– Join together to form Plexuses

• 12 pairs of Cranial nerves

• Autonomic Nervous System

 

Any localised damage to spinal cord or spinal roots will attribute to some form of functional loss.

- Paralysis: (loss of motor function)

- Parasthesias: (loss of senses)

 

The effects of disease or injury upon the CNS and periphery depend on the:

- severity of the damage

- type of neurones involved

- position of neurones involved

Lesions/Damage to the Nervous System

• Normal muscle function requires intact connections along motor pathway.

• Chain of nerve cells that runs from the brain through the spinal cord out to the muscle is called the motor pathway.

• Damage at any point reduces brain's ability to control muscle's movements.

• Reduced efficiency causes weakness (paresis).

• Complete loss of communication prevents any willed movement.

• Lack of control is called paralysis.

• Paralysis may affect an individual muscle, but usually affects an entire body region.

• Distribution of weakness an important clue to location of the nerve damage that is causing the paralysis.

• Words describing the distribution of paralysis use the suffix "-plegia," from the Greek word for "stroke.“

The types of paralysis are classified by region:

Monoplegia: affecting only one limb

Diplegia: affecting the same body region on both sides of the body (both arms, for example, or both sides of the face)

Hemiplegia: affecting one side of the body

Paraplegia: affecting both legs and the trunk

Quadriplegia: affecting all four limbs and the trunk.

• The nerve damage that causes paralysis may be in the:- brain or spinal cord (CNS)- nerves outside the spinal cord (PNS).

• The most common causes of damage to the brain are:- Stroke - Tumour - Trauma (caused by a fall or a blow) - Multiple sclerosis (destruction of Myelin

sheath)) - Cerebral palsy (defect or injury to the brain that occurs at or shortly after birth) - Metabolic disorder (interferes with body's ability to maintain itself).

• Damage to spinal cord is most often caused by trauma, (fall/car crash). Other conditions that may damage nerves within or immediately adjacent to spine include:

- Tumour

- Herniated disk (also called a ruptured or slipped disk)

- Spondylosis (a disease that causes stiffness in the joints of the spine)

- Rheumatoid arthritis of the spine

- Neurodegenerative disease (a disease that damages nerve cells)

- Multiple sclerosis.

• Paralysis originating in the brain may sometimes be flaccid, that is, the affected muscles may be loose, weak, flabby, and without normal reflexes.

• More frequently it is spastic, that is, the affected muscles are rigid and the reflexes accentuated.

• Paralysis originating in a motor nerve (UMN) of the spinal cord is always spastic

• Paralysis originating in peripheral nerves (LMN) is always flaccid.

Cerebrovascular Accident (Stroke)

• CVAs are: bleeds into the brainobstruction of blood supply to brain

• CVAs often affect Motor cortex and its major pathways.

• These tracts cross in medulla therefore:- left hemiplegia (stroke on right side of brain)- right hemiplegia (stroke on left side of brain)

• Small bleeds close to brain surface may result in weakness on one side (hemiparesis)

- good chance of recovery

• Larger/deeper bleeds may cause profound paralysis- may result in permanent damage

Pupillary Reflex

• Clinical test for brain stem function• Shine bright light into patient’s eye• Normal response: pupils constrict in response to light

stimulus• Reflex via autonomic nervous system• Sensory input of bright light- to brain via optic nerve (II)

– parasympathetic impulses out via oculomotor nerve (III) – circular muscles of eye constrict

• Pupil observation important when considering head injury care

Plantar (sole) reflex

• Tests integrity of spinal cord from L4-S2• Determines functionality of corticospinal tracts• Normal response is a downward flexion (curling) of

toes• If corticospinal tract damaged, normal plantar’s reflex

replaced by Babinski’s sign• Toes fan backwards

Normal Abnormal