Nervous system CNS, PNS and ANS in Vertebrates.pptx

Nervous system CNS, PNS and ANS in Vertebrates.pptx

1. Nervous system: CNS & PNS Dr Showkat Ahmad Wani

2. Introduction The vertebrate nervous system is one of the most advanced among animals. It is dorsal, tubular, bilaterally symmetrical , and derived from the neural tube (CNS) and neural crest cells (PNS). It enables vertebrates to perceive their environment, coordinate movements, regulate internal organs, and exhibit complex behaviors. It is divided into three major parts: Central Nervous System (CNS) – Brain and Spinal cord. Peripheral Nervous System (PNS) – Cranial and Spinal nerves. Autonomic Nervous System (ANS) – A functional part of the PNS that controls involuntary activities.

3. 1. Central Nervous System (CNS) (a) The Brain Housed in the cranium and covered by meninges and cerebrospinal fluid (CSF) . Derived from three embryonic vesicles: Forebrain (Prosencephalon): Olfactory bulbs, cerebrum, thalamus, hypothalamus. Midbrain (Mesencephalon): Optic lobes. Hindbrain (Rhombencephalon): Cerebellum and medulla oblongata. Evolutionary changes: Fishes: Large optic lobes, small cerebrum. Amphibians: Similar to fishes; cerebellum slightly more developed. Reptiles: Enlarged forebrain, improved sensory integration. Birds: Very large cerebellum and optic lobes (coordination of flight, keen vision). Mammals: Greatly enlarged cerebrum with folded cortex; advanced intelligence, memory, and emotions.

4. General Features Weight: 1.3–1.4 kg in adult humans (about 2% of body weight, but consumes ~20% of body’s energy). Protected by cranium , meninges (dura, arachnoid, pia) , and cerebrospinal fluid (CSF) . Composed of billions of neurons and glial cells. Divided embryonically into three primary vesicles : Forebrain (Prosencephalon) Midbrain (Mesencephalon) Hindbrain (Rhombencephalon )

5. Major Divisions of the Brain 1. Forebrain (Prosencephalon) Olfactory bulbs & tracts: Receive signals from nose; large in fishes & amphibians. Cerebrum (Telencephalon): Largest part in mammals. Outer layer = cerebral cortex (gray matter), highly folded in higher mammals (gyri & sulci). Functions: consciousness, memory, learning, reasoning, voluntary movements. Divided into lobes : Frontal: decision making, motor control. Parietal: sensory perception, spatial orientation. Temporal: hearing, language, memory. Occipital: vision. Diencephalon: Thalamus – relay station for sensory input. Hypothalamus – regulates homeostasis (hunger, thirst, temperature), controls endocrine system via pituitary gland. Epithalamus (pineal gland) – circadian rhythm, hormone secretion.

6. 2. Midbrain (Mesencephalon) Optic lobes / Superior colliculi: Prominent in fishes, amphibians, and birds (vision center). Cerebral peduncles: Connect forebrain with hindbrain. Functions: Coordinates vision, hearing, motor control. Reflex movements of eyes and head.

7. 3. Hindbrain (Rhombencephalon) Cerebellum: Coordinates balance, posture, and fine muscle movements. Very large in birds (flight control) and mammals (complex locomotion). Pons (in mammals): Relay center between cerebrum and cerebellum. Controls breathing rhythm. Medulla oblongata: Connects brain to spinal cord. Vital centers for heart rate, respiration, blood pressure, swallowing, vomiting.

8. Brainstem Collectively includes midbrain + pons + medulla . Controls basic life functions (breathing, heart rate, reflexes).

9. Evolutionary Trends in Vertebrate Brains Fishes: Large olfactory bulbs and optic lobes. Small cerebrum. Medulla is well-developed (vital for aquatic life). Amphibians: Similar to fishes, but cerebellum slightly larger (adaptation to both land and water). Reptiles: Enlarged cerebrum, especially in dorsal pallium. Improved sensory integration. Birds: Very large optic lobes (keen vision). Large cerebellum (flight coordination). Cerebrum relatively smooth but functionally complex. Mammals: Greatly enlarged cerebral cortex (especially neocortex). Highly folded surface (gyri, sulci) for higher intelligence. Specialization of lobes for advanced learning, speech, reasoning.

10. Special Features Corpus callosum (in placental mammals): Connects left and right cerebral hemispheres. Limbic system: Emotional processing, learning, memory (hippocampus, amygdala).

11. (Brain at a Glance) Forebrain: Intelligence, memory, sensory integration, homeostasis. Midbrain: Vision, hearing, motor coordination. Hindbrain: Balance, posture, vital life functions. Trend in evolution: progressive enlargement of cerebrum and cerebellum → higher intelligence and complex behaviors in mammals.

12. B. The Spinal Cord General Structure Long, cylindrical extension of CNS lying within the vertebral column. Protected by vertebrae, meninges, and cerebrospinal fluid (CSF) . Covered by three meninges: Dura mater (outer tough layer) Arachnoid mater (middle layer with CSF) Pia mater (inner vascular layer) Internal Organization Gray Matter (H-shaped / butterfly-shaped core): Contains neuronal cell bodies, interneurons, glial cells. Dorsal horns → sensory processing. Ventral horns → motor neurons to skeletal muscles. Lateral horns (in thoracic/lumbar) → autonomic neurons. White Matter (outer): Myelinated axons organized into tracts. Ascending tracts → carry sensory impulses to brain. Descending tracts → carry motor commands from brain.

13. Functions of the Spinal Cord Conduction Pathway Connects body with brain. Sensory impulses travel up to brain (afferent). Motor impulses travel down to body (efferent). Reflex Center Controls automatic, rapid responses without brain involvement. Example: knee-jerk reflex, withdrawal from pain stimulus . Segmental Organization Spinal cord gives rise to spinal nerves (31 pairs in mammals). Each segment processes sensory and motor inputs for its region. Evolutionary Aspect Fishes & Amphibians: Spinal cord relatively simple; less differentiation of gray and white matter. Reptiles & Birds: Increased white matter, better conduction. Mammals: Highly developed tracts, well-organized reflex centers, cervical & lumbar enlargements (to control limbs).

14. 2. Peripheral Nervous System (PNS) Cranial Nerves: 10 pairs in fishes/amphibians, 12 in reptiles, birds & mammals. Spinal Nerves: Arise from dorsal (sensory) and ventral (motor) roots of spinal cord. Functions: Connect CNS with sensory organs, muscles, skin, glands.

15. 3. Autonomic Nervous System (ANS) Part of the PNS; regulates involuntary functions . Works with hypothalamus and brainstem. Divisions: Sympathetic (thoracolumbar): “Fight or Flight” – ↑ heart rate, pupil dilation, ↓ digestion. Parasympathetic (craniosacral): “Rest and Digest” – ↓ heart rate, ↑ digestion, energy storage. Enteric System: Intrinsic nerve plexuses of gut wall (semi-autonomous).

16. Summary CNS: Brain + Spinal Cord; brain handles higher integration, spinal cord conducts and coordinates reflexes. PNS: Cranial & Spinal nerves; links CNS to body. ANS: Regulates involuntary processes (sympathetic, parasympathetic, enteric). Evolutionary trend: progressive enlargement and specialization of cerebrum and spinal tracts → increasing complexity in vertebrates.

17. Thank you