· It constitutes the Central nervous system, Peripheral nervous system and Autonomic nervous system.
A. Central Nervous System (CNS)
· It consists of the brain and spinal cord which lie in the cranial cavity and neural/spinal canal of the vertebral column respectively.
· These are covered by two membranous layers: Piamater and Dura mater.
· Piamater which is the inner one that invests the brain and spinal cord and is richly vascular.
· Duramater which is thicker and tougher.
· Space between these two layers is filled with cerebrospinal fluid.
· These are covered by two membranous layers: Piamater and Dura mater.
· Piamater which is the inner one that invests the brain and spinal cord and is richly vascular.
· Duramater which is thicker and tougher.
· Space between these two layers is filled with cerebrospinal fluid.
1. Brain
· It is elongated and bilaterally symmetrical.· Divisible into 3 parts: Forebrain, Midbrain and Hindbrain.
A) Forebrain/Prosencephalon:
· Consists of olfactory lobe, cerebral hemispheres and diencephalon.
a. Olfactory lobes
- Anterior, elongated, oval structures and united together at midline.
- Anterior ends receive the olfactory nerves.
- Cavity present: Olfactory ventricle or Rhinocoel.
- Anterior, elongated, oval structures and united together at midline.
- Anterior ends receive the olfactory nerves.
- Cavity present: Olfactory ventricle or Rhinocoel.
- It controls the sense of smell but in frogs, it is very poor.
b. Cerebral hemispheres
- Not completely fused in the midline.
- Not completely fused in the midline.
- Two hemispheres are separated by a median longitudinal fissure.
- Cavity present: 1st and 2nd or Lateral ventricle or Paracoel.
- Cavity present: 1st and 2nd or Lateral ventricle or Paracoel.
- Ventral surface of each cerebral hemisphere: Corpus striatum → joined to each other by anterior commissure.
- Roof of the cerebrum is called pallium but its thick ventrolateral sides are called corpora striata.
- Roof of the cerebrum is called pallium but its thick ventrolateral sides are called corpora striata.
c. Diencephalon (Thalamencephalon)
- Diamond-shaped structure between cerebral hemispheres and mid-brain.
- Lateral walls: thick → called Optic thalami and its thick floor is the hypothalamus.
- Cavity present: 3rd ventricle or Diocoel.
- Diamond-shaped structure between cerebral hemispheres and mid-brain.
- Lateral walls: thick → called Optic thalami and its thick floor is the hypothalamus.
- Cavity present: 3rd ventricle or Diocoel.
- Posterior dorsal side bears a pineal stalk and the pineal body.
- The pineal body is connected to the stalk in the tadpole but is separate and lies outside the skull as the Brow spot or the Third eye.
- Roof of diencephalon: Anterior choroids plexus.
- The pineal body is connected to the stalk in the tadpole but is separate and lies outside the skull as the Brow spot or the Third eye.
- Roof of diencephalon: Anterior choroids plexus.
- The floor of the diencephalon: optic chiasma, infundibulum and the pituitary body.
B) Mid-brain or Mesencephalon
- Broadest part of the brain.
- Consists of two large hollow lobes called Optic lobes.
B) Mid-brain or Mesencephalon
- Broadest part of the brain.
- Consists of two large hollow lobes called Optic lobes.
- It is also called corpora bigemina
- Cavity present: Optic ventricles or Optocoels.
- Optocoel communicates with paracoels by Foramen of Monro and Metacoel or Fourth ventricle by Aqueduct of Sylvius or Iter.
- Floor is formed by two longitudinal ridges called Crura cerebri or Cerebral peduncles, which carry stimuli from cerebral hemispheres to the medulla oblongata.
- Optic nerves arise from the ventral surface of the optic lobes and cross each other to form Optic chiasma.
· Between diencephalon and two optic lobes: Posterior commissure.
C) Hind-brain or Rhombencephalon:
- Cavity present: Optic ventricles or Optocoels.
- Optocoel communicates with paracoels by Foramen of Monro and Metacoel or Fourth ventricle by Aqueduct of Sylvius or Iter.
- Floor is formed by two longitudinal ridges called Crura cerebri or Cerebral peduncles, which carry stimuli from cerebral hemispheres to the medulla oblongata.
- Optic nerves arise from the ventral surface of the optic lobes and cross each other to form Optic chiasma.
· Between diencephalon and two optic lobes: Posterior commissure.
C) Hind-brain or Rhombencephalon:
· Consists of the Medulla oblongata and cerebellum.
· Cerebellum
- Lies across the roof in the anterior part of the fourth ventricle.
- Solid, No cavity.
- Poorly developed in the frog.
- It controls muscular coordination and equilibrium in frogs.
· Medulla oblongata
- It is the posterior conical part of the brain.
- Cavity present: Fourth ventricle/Metacoel →continuous with the central canal of the spinal cord.
- Roof: Posterior choroid plexus.
- CN5 – CN10 originate from the medulla.
Functions of the various parts of the brain:
a. Olfactory lobes: Sense of smell.
b. Cerebral hemispheres
· Intelligence
· Voluntary control
c. Diencephalon: Regulation of temperature, reproductive functions and chemical actions during digestion and sleep.
d. Optic lobes: Sight, spontaneous movements.
e. Cerebellum: Equilibrium of body (automatic movements, regulation of voluntary movements).
f. Medulla oblongata: Autonomic vital functions like:
· Snapping reflex during catching prey
· Croaking reflex
· Protrusion of tongue
· Swallowing reflex
· Respiratory movements
· Locomotion
· It continues from the medulla oblongata through the foramen of magnum or occipital foramen.
· End of spinal cord tapers and forms a thread-like portion: Filum terminale → lies within the urostyle (10th vertebra).
· A number of nerve roots arise from the terminal portion → Cauda equina.
· Two swollen parts along its length:
· Brachial enlargement lies in between forelimbs: supplies forelimbs
· Sciatic/Lumbar enlargement lies below filum terminale: supplies hind limbs.
· Two longitudinal grooves on dorsal and ventral sides: Dorsal sulcus and ventral fissures.
· Narrow canal at centre: Central canal or Canalis centralis.
· Around the central canal: Gray matter – consists of dorsal and ventral horns.
· Outside grey matter: White matter.
· Functions of Spinal Cord:
a) Pathway for sensory stimuli.
b) Centre for reflex action.
A. Cranial nerves: 10 pairs
a) Olfactory: Sensory
A. Sympathetic Nervous System
· It includes 2 ganglionated nerve cords (sympathetic trunks) which are developed on either side of the spinal cord.
· Number of ganglia in each trunk is 30 which are connected with adjacent spinal nerves by small nerves called ramus communicans
· Each chain enters the skull through the 10th vagus nerve & end at the Gaserian ganglia of the trigeminal nerve.
· Nerve fibres of the sympathetic system enter into the circulatory system, digestive system and glandular organs.
· Therefore it stimulates their working by releasing the chemical called sympathin, especially in emergency conditions.
B. Parasympathetic Nervous System
· It consists of small ganglia present near the visceral organs which are communicated to some cranial nerves and spinal nerves.
· It helps to return to the body at normal condition by releasing acetylcholine.
· Sympathetic and parasympathetic have antagonistic functions.
· Cerebellum
- Lies across the roof in the anterior part of the fourth ventricle.
- Solid, No cavity.
- Poorly developed in the frog.
- It controls muscular coordination and equilibrium in frogs.
· Medulla oblongata
- It is the posterior conical part of the brain.
- Cavity present: Fourth ventricle/Metacoel →continuous with the central canal of the spinal cord.
- Roof: Posterior choroid plexus.
- CN5 – CN10 originate from the medulla.
Functions of the various parts of the brain:
a. Olfactory lobes: Sense of smell.
b. Cerebral hemispheres
· Intelligence
· Voluntary control
c. Diencephalon: Regulation of temperature, reproductive functions and chemical actions during digestion and sleep.
d. Optic lobes: Sight, spontaneous movements.
e. Cerebellum: Equilibrium of body (automatic movements, regulation of voluntary movements).
f. Medulla oblongata: Autonomic vital functions like:
· Snapping reflex during catching prey
· Croaking reflex
· Protrusion of tongue
· Swallowing reflex
· Respiratory movements
· Locomotion
2. Spinal Cord
· It is the posterior continuation of the medulla oblongata, somewhat flattened dorsoventrally.· It continues from the medulla oblongata through the foramen of magnum or occipital foramen.
· End of spinal cord tapers and forms a thread-like portion: Filum terminale → lies within the urostyle (10th vertebra).
· A number of nerve roots arise from the terminal portion → Cauda equina.
· Two swollen parts along its length:
· Brachial enlargement lies in between forelimbs: supplies forelimbs
· Sciatic/Lumbar enlargement lies below filum terminale: supplies hind limbs.
· Two longitudinal grooves on dorsal and ventral sides: Dorsal sulcus and ventral fissures.
· Narrow canal at centre: Central canal or Canalis centralis.
· Around the central canal: Gray matter – consists of dorsal and ventral horns.
· Outside grey matter: White matter.
· Functions of Spinal Cord:
a) Pathway for sensory stimuli.
b) Centre for reflex action.
B. Peripheral nervous system (PNS)
· It consists of cranial nerves and spinal nerves.A. Cranial nerves: 10 pairs
a) Olfactory: Sensory
b) Optic: Sensory
c) Occulomotor: Motor
c) Occulomotor: Motor
d) Trochlear: Motor
e) Trigeminal: Mixed
f) Abducens: Motor
e) Trigeminal: Mixed
f) Abducens: Motor
g) Facial: Mixed
h) Auditory: Sensory
h) Auditory: Sensory
i) Glossopharyngeal: Mixed
j) Vagus: Mixed
B. Spinal nerves:
j) Vagus: Mixed
B. Spinal nerves:
· 9 pairs in Rana tigrina (Exception).
· In other species of frogs, usually they are 10 pairs.
· As the nerve roots (dorsal and ventral) arise from the vertebral column, the root is covered with calcareous mass known as glands of Swammerdam or periganglionic glands.
· The roots unite to form a small branch which soon divides into 3 branches:
a. Dorsal branch (Ramus dorsalis) → Skin and muscles of the dorsal body wall.
b. Ventral branch (Ramus ventralis) →Skin and muscles of ventral body wall and limbs.
c. Ramus communicans → Joins sympathetic cord.
· All the spinal nerves are mixed.
· 1st (hypoglossal) → Muscles of the tongue, the floor of the buccal cavity, shoulder, back.
· As the nerve roots (dorsal and ventral) arise from the vertebral column, the root is covered with calcareous mass known as glands of Swammerdam or periganglionic glands.
· The roots unite to form a small branch which soon divides into 3 branches:
a. Dorsal branch (Ramus dorsalis) → Skin and muscles of the dorsal body wall.
b. Ventral branch (Ramus ventralis) →Skin and muscles of ventral body wall and limbs.
c. Ramus communicans → Joins sympathetic cord.
· All the spinal nerves are mixed.
· 1st (hypoglossal) → Muscles of the tongue, the floor of the buccal cavity, shoulder, back.
· 2nd, 3rd (+1st) → Branchial plexus.
· 4th, 5th, 6th → Body wall of the belly region.
· 7th, 8th, 9th → Sciatic plexus
· 10th → Coccygeal nerve.
· 4th, 5th, 6th → Body wall of the belly region.
· 7th, 8th, 9th → Sciatic plexus
· 10th → Coccygeal nerve.
C. Autonomic nervous system (ANS)
· It consists of the sympathetic and parasympathetic nervous systemA. Sympathetic Nervous System
· It includes 2 ganglionated nerve cords (sympathetic trunks) which are developed on either side of the spinal cord.
· Number of ganglia in each trunk is 30 which are connected with adjacent spinal nerves by small nerves called ramus communicans
· Each chain enters the skull through the 10th vagus nerve & end at the Gaserian ganglia of the trigeminal nerve.
· Nerve fibres of the sympathetic system enter into the circulatory system, digestive system and glandular organs.
· Therefore it stimulates their working by releasing the chemical called sympathin, especially in emergency conditions.
B. Parasympathetic Nervous System
· It consists of small ganglia present near the visceral organs which are communicated to some cranial nerves and spinal nerves.
· It helps to return to the body at normal condition by releasing acetylcholine.
· Sympathetic and parasympathetic have antagonistic functions.
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