Chapter 21: Neural Control and Coordination - Class 11 Biology Notes PDF for NEET 2027

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NEET Biology Chapter 21: Neural Control and Coordination

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Brain + Neuron + Reflex + Disorders

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### *Chapter 21: Neural Control and Coordination*

### *1. Neural System in Humans*

*Functions*: Point-to-point coordination, Fast, Voluntary + Involuntary actions

*2 Parts:*

1. *Central Neural System CNS*: Brain + Spinal Cord

2. *Peripheral Neural System PNS*: All nerves of body

*PNS is further divided:*

- *Somatic Neural System SNS*: Voluntary. Transmits impulses from CNS to skeletal muscles

- *Autonomic Neural System ANS*: Involuntary. Controls visceral organs  

    - *Sympathetic*: Fight & Flight 

    - *Parasympathetic*: Rest & Digest

- *Visceral Neural System*: Part of ANS. Inner organs

### *2. Neuron - Structural & Functional Unit of Neural System*

*Parts of Neuron:*

1. *Cell body / Cyton*: Contains nucleus, Nissl's granules. Protein synthesis

2. *Dendrites*: Short branches. Receive impulses

3. *Axon*: Long process. Conducts impulse away from cell body

      - *Axon hillock*: Impulse generating site

      - *Myelin sheath*: Formed by Schwann cells. Speeds up conduction

      - *Nodes of Ranvier*: Gaps in myelin. Saltatory conduction

      - *Axon terminals*: Release neurotransmitters

*Types of Neurons:*

1. *Sensory/Afferent*: PNS → CNS

2. *Motor/Efferent*: CNS → PNS

3. *Interneurons/Association*: CNS me hi. Connect sensory & motor

### *3. Generation and Conduction of Nerve Impulse*

*Resting Membrane Potential*: -70mV. Due to more Na⁺ outside, more K⁺ inside

*Steps:*

1. *Stimulus* → Na⁺ channels open → Na⁺ influx

2. *Depolarization*: Membrane becomes +30mV. This is *Action Potential*

3. *Repolarization*: K⁺ channels open → K⁺ efflux → Back to -70mV

4. *Refractory period*: No new impulse

*Conduction:*

- *Unmyelinated*: Continuous conduction

- *Myelinated*: *Saltatory conduction*. Impulse jumps from one node to next. Faster

### *4. Transmission of Impulses*

*Synapse*: Junction between 2 neurons

*2 Types:*

1. *Electrical Synapse*: Gap junctions. Faster. Rare in humans

2. *Chemical Synapse*: Synaptic cleft present. Neurotransmitters used

*Events at Chemical Synapse:*

1. Action potential reaches axon terminal

2. *Ca²⁺ influx* → Synaptic vesicles fuse

3. *Neurotransmitter release* - Ex: Acetylcholine, Noradrenaline

4. Binds to receptors on next neuron → Opens ion channels

5. *Excitatory*: Generates AP. *Inhibitory*: Prevents AP

6. Neurotransmitter degraded/reabsorbed

### *5. Central Neural System - Brain*

*Human Brain*: Protected by *Cranium*. Covered by *3 Meninges*: Dura mater, Arachnoid, Pia mater

*Divided into 3 parts:*

#### *A. Forebrain*

1. *Cerebrum*: Largest part. 2 cerebral hemispheres. Outer cortex = grey matter, inner = white matter

      - *Functions*: Sensory perception, Memory, Intelligence, Voluntary motor control, Speech

      - *Fissures*: Central, Lateral, Parieto-occipital

      - *Lobes*: Frontal, Parietal, Temporal, Occipital

2. *Thalamus*: Relay center. Sensory signals → Cerebrum

3. *Hypothalamus*: Base of thalamus. 

      - *Functions*: Thermoregulation, Hunger, Thirst, Sleep, Osmoregulation

      - Controls pituitary. Produces hormones

*Limbic System*: Hippocampus + Amygdala + Others. *Center for emotions*, memory, sexual behavior

#### *B. Midbrain*

Between thalamus & pons. 

- *Corpora quadrigemina*: 4 lobes. Visual & auditory reflex

- *Cerebral peduncles*: Connect fore, mid & hind brain

#### *C. Hindbrain*

1. *Pons*: Part of brainstem. Connects different brain regions

2. *Cerebellum*: 2nd largest. Below cerebrum

      - *Function*: Coordination, Balance, Posture, Fine muscle movements

3. *Medulla Oblongata*: Connects brain to spinal cord

      - *Functions*: Respiration, Heartbeat, Gastric secretions, Blood pressure

### *6. Spinal Cord*

- Extends from medulla. Enclosed in vertebral column

- *Functions*: Reflex actions, Conduction of impulses to & from brain

- *Grey matter*: Inner, H-shaped. *White matter*: Outer

### *7. Reflex Action*

*Definition*: Sudden, involuntary response to stimulus

*Reflex Arc*: Receptor → Sensory neuron → CNS → Motor neuron → Effector  

*Example*: Touching hot object → Hand withdraws

### *8. Disorders of Neural System*

1. *Alzheimer's disease*: Degeneration of neurons. Memory loss

2. *Parkinson's disease*: Dopamine deficiency. Tremors, rigidity

3. *Epilepsy*: Abnormal electrical activity. Seizures

4. *Multiple sclerosis*: Myelin sheath destruction

5. *Meningitis*: Inflammation of meninges

### *9. NEET High Yield Points*

- *Nissl's granules*: Ribosomes + RER in cyton. Absent in axon

- *Synaptic cleft*: 20-40 nm wide

- *Neurotransmitter*: ACh - Excitatory in somatic, Inhibitory in ANS

- *Cerebrum* = Seat of intelligence

- *Cerebellum* = Seat of coordination

- *Medulla* = Vital center

- *Hypothalamus* = Master of endocrine system

- *Corpus callosum*: Connects 2 cerebral hemispheres

- *White matter*: Myelinated axons. *Grey matter*: Cell bodies

Revise this + *NCERT Brain diagram* 2 baar. *Brain parts + Neuron + Reflex arc* se har saal 2 questions aate hain 💯