Topic 9 Control and Coordination
Parts of the brain
There are three divisions of the brain, viz. forebrain (prosencephalon), midbrain mesencephalon) and hindbrain (rhombencephalon).
A.Forebrain is divided into cerebrum (telencephalon) and
diencephalon (thalamencephalon). Underdeveloped olfactory lobes (rhinencephalon)
can also be seen in the anterior region.
B.Midbrain consists of corpora quadrigemina and crura cerebri.
C.Hindbrain has cerebellum (metencephalon) and brain stem. It is
divided into pons varolii and medulla oblongata (myelencephalon).
A. Forebrain :
Forebrain consists of olfactory lobes,
cerebrum and diencephalon.
Parts of the Forebrain (Prosencephalon) &
functions.
i)Olfactory lobes (Rhinencephalon)
Paired, small bodies, lying ventrally in the
forebrain
Two parts :
Olfactory bulbs and olfactory tracts
Functions :
Sense of smell
ii)Cerebrum (Telencephalon) 85% of brain
Structure associated :
- Corpus callosum : band connecting two hemispheres.
- Pallium :
Roof of brain.
- Corpora striata : Ventro lateral walls.
Peculiarities :
Cerebral fissure divides it into two cerebral
hemispheres.
Outer cortex, inner medulla.
Gyri-ridges and sulci-depressions
Three deep sulci :
- Central
which demarcates frontal lobe from the parietal lobe.
- Lateral sylvian
sulcus demarcates the temporal lobe from the frontal and parietal lobes
- parieto-occipital. separates the parietal from occipital lobe.
Four lobes of cerebrum :
- Anterior frontal
- Middle parietal
- Posterior occipital
- Lateral temporal
Functional areas of cerebrum
cerebrum, thus shows all three types of areas
sensory, motor and association area.
Frontal lobes
Controls voluntary motor activities or
movements of muscles.
Centre for involuntary movements and
autonomus nervous system.
Coordination between sensation and movements.
Broca’s area/motor speech area. It translates the thoughts into
speech.
Expression of emotions, intelligence,
willpower, memory, personality areas are located in the frontal lobe.
Parietal lobes
Somaesthetic sensation of pain,
pressure,temperature, taste (gustatoreceptor).
Temporal lobes
smell (olfactory), hearing (auditory), speech
and emotions.
Occipital lobes
sense of vision.
Area of contact between temporal, parietal
and occipital lobes is centre for Wernicke’s area or intelligence centre.
iii) Diencephalon (Thalamencephalon) :
Structure associated :
- Epithalamus : Roof has anterior choroid plexus.
- Thalamus .
- Hypothalamus Floor of diencephalon
- It lies below the corpus callosum and above the midbrain.
- It encloses a single cavity termed third
ventricle/Diocoel which communicates with the two lateral ventricles of
cerebrum through a narrow opening called foramen of Monro.
1. Epithalamus
- Non nervous roof of the diencephalon
- Anterioly it is fused with the piamater to form the anterior choroid plexus and from its dorsal wall it is connected to pineal gland through a pineal stalk
- The lateral thick walls of diencephalon form the thalami.
- They mainly contain grey matter
RAS (Reticular Activating System)
- It is called relay centre as it transmit all sensory impulses except those of olfactory (smell) to the cerebrum
- The narrow cavity of diencephalon is called IIIrd ventricle or diocoel.
- It connects anteriorly to the two lateral ventricles by a single opening called Foramen of Monroe and posteriorly to the IVth ventricle or metacoel through a narrow duct of Sylvius or iter.
2. Hypothalamus :
- It forms a floor of the diencephalon.
- It is richly supplied with blood vessels (Hypothalamo-hypophyseal portal vein) helps in feed back mechanism for hormonal control).
- It maintains homeostasis, internal equilibrium of the body and involuntary behaviour control.
- link between the nervous and the endocrine system
Limbic system A complex neuronal circuit is formed by the
hypothalamus amygdala, parts of epithalamus and thalamus, hippocampus and other
areas.
It appears to be responsible for emotional
reactions, motivational drives and memory.
Hypopyseal stalk or infundibulum
The floor of the hypothalamus continues as a
downward projection which connects it to the hypophysis (pituitary gland) both
physically and functionally by secretion of neurotransmitters
The inferior surface of hypothalamus also
bears the
Optic chiasma:- crossing of the two optic nerves)
Pair of mammillary bodies:- unique to mammalian brain and responsible
for recollective memory.
Functions of diencephalon:
- Diencephalon acts as a relay centre for motor and sensory impulses between spinal cord, brainstem and various areas of cerebral cortex.
- Diencephalon consists of epithalamus, thalami and hypothalamus.
- Therefore it acts as a centre for homeostasis and higher centre of autonomous nervous system.
- Hypothalamic nuclei secrete neurohormones which influence the pituitary gland.
- Diencephalon regulates heartbeats, blood pressure and water balance.
- Anterior choroid plexus which is located in the diencephalon secretes cerebrospinal fluid.
- Hypothalmic regions control many involuntary functions such as hunger, thirst, thermo-regulation, fear, anger, sleep, sexual desire, etc.
B.Mid brain
- Located between diencephalon and the pons varolli.
- Cerebral aqueduct or iter that connects the third and fourth ventricles.
Parts of the Midbrain (Mesencephalon)
i) Corpora quadrigemina :
Two pairs of lobes.
- 1st pair superior colliculi : Receives optic nerves.
- 2nd pair inferior colliculi : Receives auditory nerves.
- Operate when it is necessary to move the head to hear sounds more distinctly.
ii) Cerebral peduncles or crura cerebri
- Tracts of ascending and descending nerve fibres from RAS and connect the cerebrum mid brain
- Present at inferior surface of Mid brain
Red nucleus
- Present at Centre of the mid brain
- Important role in controlling posture and muscle tone, modifying some motor activities and motor coordination.
C. Hind brain (Rhombencephalon)
- The posterior region of the brain is called hind brain
- Parts of the Hindbrain
- Cerebellum (Metencephalon)
- Pons Varolii :
- Medulla oblongata (Myelencephalon) :
Cerebellum (Metencephalon) :
- 11% of the brain second largest region.
- Structure associated :
- Arbor vitae : Tree like processes of inner white matter extending into the outer grey matter.
Peculiarities :
- Posterior most part.
Three lobes : Median vermis, two lateral cerebellar
hemispheres.
Functions of Cerebellum :
- Cerebellum is a primary centre for the control of equilibrium, posture,
- balancing and orientation.
- Neuromuscular activities are regulated by the cerebellum.
- Coordination of walking, running, speaking, etc. is under the control of hind brain.
Pons Varolii :
- Nerve fibres that form bridges between cerebrum and medulla oblongata.
- Outer white and inner grey matter.
- Nerve fibres cross over here.
Functions of Pons :
- Activities of two cerebellar hemispheres are coordinated by pons.
- Nerve fibres cross over in this area and thus the right side of the brain controls
- the left part of the body and vice versa.
- Pons controls the consciousness of the brain.
- Breathing centre is located in pons along with medulla.
Medulla oblongata (Myelencephalon) :
- Posterior most part that continues as a spinal cord.
- Outer white and inner grey matter.
- It has a posterior choroid plexus.
- Cranial nerves arise from medulla.
Functions of Medulla oblongata :
- Medulla oblongata controls all the involuntary activities such as heartbeats,
- respiration, vasomotor activities.
- Peristalsis and reflex actions such as coughing, sneezing, swallowing, etc. are also under the control of medulla oblongata.
- Medulla oblongata is essential for all the vital functions of the body.
Ventricles of brain
- Ventricles are the cavities present in different parts of the brain.
- There are four ventricles in the human brain. All the ventricles are connected with each other.
- They are filled with cerebrospinal fluid.
Paracoel or lateral ventricles-I and-II are present
inside the cerebral hemispheres.
The diencephalon has ventricle-III.
Ventricle-III is in connection with lateral
ventricles by foramen of Monro.
Spinal Cord
- Spinal cord is the part of central nervous system and forms the lower extension of the medulla oblongata of the brain.
- It lies within the neural canal of the vertebral column and is surrounded by three meninges.
- Externally, the spinal cord appears as long cylindrical rod.
- It is 42 to 45 cm long and 2.0 to 2.5 cm broad.
Conus medullaris: Terminal nervous part of the spinal cord.
Filum terminale : Thread like non-nervous extension.
Cauda equina — Filum terminale with some spinal nerves
running parallel to it. (Appearing like a horse-tail)
31 pairs of spinal nerves arise from lateral
sides of the spinal cord.
T. S. of spinal cord
- The spinal cord has a deep, narrow dorsal fissure and a broad ventral fissure.
- The inner grey matter is H-shaped and the outer white matter surrounds it.
- Grey matter is divisible into six horns, namely dorsal, lateral and ventral horns.
- The white matter is divisible into 6 columns or funiculi, namely dorsal, lateral and ventral funiculi.
- The dorsal and ventral horns extend out of the spinal cord as dorsal root and ventral root.
- The dorsal root has dorsal root ganglion which is a collection of unipolar sensory neurons. No such ganglia on ventral root.
- The adjustor/association or inter-neurons lie inside the grey matter.
- The white matter consists mainly of bundles of myelinated nerve fibre called
- ascending and descending tracts.
Functions:
The spinal cord is the main centre for the
most reflex actions.
It provides pathway for conduction of sensory
and motor impulses.
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