central nervous system (cns)

CENTRAL NERVOUS SYSTEM (CNS)

Dr Than Kyaw4 December 2011

Physiology I

Lecture-outline

• Gross anatomy of the brain• General functions• limbic system• Motor system, UMN and LMN• Spinal reflex• Vestibular apparatus and postural control

Parts of the Brain

1. Cerebrum - 2 pairs (cerebral

hemisphere)

Cortex (gray)Medulla (white)Basal nuclei

2. Cerebellum (unpaired)

3. Brain stem

(a) Interbrain

Pituitary glandHypothalmusSubthalmusThalmusepithalmus

(b) Midbrain

(c) Pons

(d) Medulla oblongata

Sheep brain

Gyrus/ridgeFissure/sulcus

Sheep brain : sagittal section

Sheep brain : Ventral view

Peripheral Nervous system

A. Cranial nerves12 – pairs 11 pairs – in head 1 pair – in head and stretches up to visceral organs (Vagus nerve)

B. Spinal nerves - in pairs - numbers vary with species

I Olfactory (smell)II Optic (Retina; Vision)III Oculomotor (Most ms of eye)IV Trochlear (eye: dor obl ms)V Trigeminal (eye, face, ms of mastication)VI Abducens (retractor, lateral eye ms)VII Facial (ear, taste, salivary glands, facial ms)VIII Vestibulocochlear (hearing, equilibrium)IX Glossopharyngeal (pharynx, tongue)X Vagus (Pharynx, larynx, visceral structures

in the thorax and abdomen)XI Accessory (MS of shoulder and neck)XII Hypoglossal (Tongue ms)

Cranial nerves

Functions of the brain cerebral cortex Gray matter – most of neuronal cell bodies

- unlike spinal cord – it lies on the exterior- Voluntary movement (initiation)

- impulses from the areas in one hemisphere cause movement of muscle on the opposite side of the body

- Sensations brought into conscious- Higher functions – educational, reasoning, planning

- Specific sensory areas (centers)- body sense areas – receives impulses from the skin

(touch, warmth, cold, pain localization)- receives impulses from muscle, tendon,

joints - impulses from eye (sight), ear (hearing), nose (smell), tongue (taste),

Dog Brain – Cross-section of Cerebral Hemispheres

Grey matter

Basal nuclei

white matter

Corpus callosum

Lateral ventricles

Cerebral cortex and its functions

White matter – beneath gray matter - contain myelinated nerve fibers connecting

different parts of the cortex, 2 hemis-spheres, other parts of

the brain and spinal cord

Basal neuclei – lie deep within cerebral hemispheres (Basal ganglia) - composed large pool of neurones

- control complex semi-voluntary movements - e.g. walking, running, vomitting

Cerebellum- Not concerned with sensation and consciousness- Concerned with automatic adjustment to prevent distortion of inertia

and momentum (balance and posture)

Interbrain- Hypothalmus – consists of pituitary gland (endocrine gld)

- Complex sensing and neurosecretory functions - Centers for thermoregulation, hunger, thirst, sleep patterns,

sex drive

- Thalmus – relay center: impulses from all areas of the body are transmitted to thalmus for transfer to the cerebral cortex

- Epithalmus – olfactory correlation center - pineal gland: gonadal hormone

Mid brain- Auditory reflex centers- Visual reflex centers- Several descending tracts

Pons

- Main function - relay center for many signals to and from the cerebrum, cerebellum and spinal cord

Medula oblongata

- Many ascending and descending pathways

- Sensory and motor nuclei for ten cranial nerves originated

- A large part of central mechanism of postural reflexes (hopping,

righting, placing)

- Vital regulatory centers

- heart rate, vasomotor tone (bld v/s muscles) Blood pressure,

respiration,

- Contain reflexes

- motor swallowing, coughing, vomitting, sneezing and secretory

activities of the digestive tract

- Components of limbic system

the cortex,

Cingulate gyrus

Hippocampus

hypothalamus, thalamus,

Amygdala and

basal nuclei (several areas deep within the cerebrum)

Limbic System

Functions of limbic systemBehavior and control of our behaviorEmotions

- nature of the sensations, pleasant or unpleasant- rage, fear, anger, pain, pleasure, sorrow- This helps guide the individual into appropriate behavior

that is more likely to be beneficial (survival).- Learning and memory

All these functions are controlled through the Reward and punishment function of the limbic system.Reward (satisfaction)

e.g satisfiction after eating, drinking, success…etc

Punishment (displeasure, fear, terror, pain..etc)

- Limbic system - involved in memory formation

- Hippocampus, structure deep in the cerebrum and a part of limbic system - necessary to form new memories

- Damage of hippocampus - cannot remember things since the time the damage occurred but can remember from before that time.

- Short-term memory - probably stored as electrical differences because they can be removed by the application of an electrical shock.

- Long-term memory - probably stored as new or different synapses. Research shows that learning is associated with an increased number of synapses. Forgetting is associated with a decreased number.

Memory

Motor neurons Two types:

1. Upper motor neurons (UMNs) 2. Lower motor neurons (LMNs)

Somatic motor neurons (include both UMN &LMN)

- Cell bodies within CNS - Their axons extend from CNS to contact skeletal. - carry motor information down to the final common

pathway (any motor neurons that connects to a muscle)

Upper and Lower Motor Neurons

Lower Motor Neurone (red line)

Upper motor neurons (UMNs)

• Motor neurons within CNS• Regulate the activity of a LMN• Initiate voluntary movement• maintain relatively stable body posture and balance

Upper motor neuron lesions

• Reflexes and voluntary activity possible but abnormal • Decreased control of active movement, particularly slowness• Babinski sign (human): big toe is raised (extended) rather than

curled downwards (flexed) upon appropriate stimulation of the sole of the foot.

Lower motor neurons (LMNs) - The nerves connecting the spinal cord to the muscles- Relay the movement instructions provided by the UMN, to the muscles

A lower motor neuron lesion

Symptoms - Muscle paresis/paralysis, hypotonia/atonia, hyporeflexia/areflexia - The extensor Babinski reflex is usually absent. - End-stage muscle denervation: Muscle wasting, fasciculations

Causes - Common causes: injuries by trauma to peripheral nerves

Spinal Cord

- Run inside the vertebral column

- Paired spinal nerves from the vertebrae

- receive sensory afferent fibers (dorsal root)

- gives off motor efferent fibers (ventral root)

Spp Cervical Thoracic Lumber Sacral Caudal

Dog 7 13 7 3 20 (avg)

Cat 8 13 7 3 7

Cow 7 13 6 5 18-20

Pig 7 11-15 6-7 4 20-23

Man 7 12 5 5 2

Horse 7 18 6 5 15-21

Sheep 7 13 6-7 4 16-18

Chicken 7 7 14 (lumboscral)

Number of vertebrae

Spinal nerves = Number of vertebrae x 2

Spinal Cord

- Gray matter – nerve cell bodies and processes

- White matter – bundles of nerve fibers having common

origin, termination and function; these bundles connect

brain stem and higher centers with spinal nerves

(Efferent, motor)

(Afferent, sensory)

Grey matter White matter

ventral median fissure

Dorsal horn

lateral funiculus

ventral funiculus

Dorsal funiculus

Cross section of spinal cord : dog; C2 region

- Dendrites ("tree branches") receive info from other neurons

- The axon conducts the impulse to other neurons via axon terminals

- Types of specialized neurons- afferent (sensory) neurons- interneurons (only connecting to other neurons)- motor neurons.

Reflex and Reflex arc

- A reflex is a rapid automatic response to a stimulus

- An accidental touch to a hot object automatic jerk of hand away- Automatic blinking when an object approaches the eye - Cats twist their bodies in the air when falling so they land on their paws- sneezing- the constriction of the pupil of the eye in bright light

A reflex arc: the path taken by the nerve impulses in a reflex

Components of a reflex arc

- A receptor- An afferent limb- central connection- An efferent limb- An effector organ

Spinal reflex e.g. The knee jerk reflex

- A stretch receptor in the extensor muscle (patellar ligament) reports the hammer tap to the vertebral column by neurons.

- Those connect to motor neurons that return to the muscle and make it flex.

- A spinal interneuron also receives the nerve impulse and connects to another set of motor neurons that inhibit the antagonistic muscle.

Reflex centers

• Located throughout the CNS• Simplest reflex

– associated with the spinal cord• Complex reflex

– carried out through reflex center in the brain- medulla oblongata and pons (e.g. swallowing, H/R)

- cerebellum – centers associated with locomotion and postures

- hypothalmus – regulatory centers; e.g temperature - midbrain – visual and auditory reflexes

- produced by the choroid plexus tissue located within the brain - flows through a series of cavities (ventricles) out of the brain and down along the spinal cord- CSF is kept separate from the blood supply by the blood-brain barrier.

Cerebrospinal fluid

Lateral ventricle