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