Coordination — Short Questions

Any factor in external or internal environment, which can initiate a response in the body is called a stimulus.

Examples Touch, light, sound, heat, cold, pressure, infection etc are the stimuli.

Sensory Neurons Sensory Neurons transmit nerve impulses from receptors to the CNS. It transmits signals to the central nervous system (CNS) from sensory organs (touch, sight, etc. ).

Motor Neuron Motor Neuron transmits nerve impulse from inter-neuron to effector (Muscles or glands) for production of response.

Inter-neurons Inter-neurons are present in brain and spinal cord. They receive impulses from sensory neurons and transmit them to motor neurons.

Reflex Action Reflex actions are the quick involuntary response in which brain is not involved. Reflex actions are controlled by a reflex arc.

Reflex Arc A reflex arc is the pathway of neurons over which the nerve impulses travel during a reflex action.

(a) Dendrite and axon
Dendrite: Small branches which project from the cell body are called dendrites. They transmit nerve impulses towards cell body.

Axon Axon is a long branch from cell body Its terminal and is further branches. Axon transmits nerve impulses from cell body to other neurons, muscles or glands.

(b) Cerebrum and Cerebellum
Cerebrum: It is the largest part of the human brain. Cerebrum is the main centre of various sensations e.g., hearing, sight, smell, memory, involuntary action, intelligence and reasoning.

Cerebellum It is the second largest part of the brain. It controls balance and muscle coordination.

(c) Thalamus and Hypothalamus
Thalamus: It is a structure wrapped by the cerebrum. It conveys information coming from receptors to the cerebrum. Thalamus is also involved in pain perception and consciousness.

Hypothalamus It lies above midbrain and just below thalamus. In humans, it is about the size of an almond. It regulates body temperature, hunger, thirst, and emotional states.

[Diagram showing neuron with labeled parts including Dendrite, Node of Ranvier, Cell body, Axon Terminals, Schwann cell, and Myelin Sheath]

[Diagram showing cross-section of spinal cord with labeled parts: Dendrite, Node of Ranvier, Cell body, Axon Terminals, Schwann cell, Myelin Sheath for neuron structure, and Axon of Sensory neuron, Dorsal root, Inter neuron, Ganglion, Spinal nerve, Axon of motor neuron, Ventral root, Grey matter, and White matter for the cord structure]

The neurons differ in their structure and in direction toward which they carry impulses.

Sensory Neurons They carry sensory information from receptor to the brain and spinal cord. It has one dendrite and one axon.

Motor Neurons They carry impulses from the brain and spinal cord to the effectors. They have many dendrites and one axon.

Interneurons These are found in brain and spinal cord. They have many dendrites and axons. The interneuron carries impulses from sensory neuron to motor neuron.

Yes, nerve impulses only travel in one direction in neurons. This impulse transmission is dependent on synaptic transmission. This happens because nerve cells only have one-transmission site. The receptors also work in one direction.

The functions performed by each part of the body are coordinated. This coordination is brought about by the organ system called nervous system.

(i) The nervous system regulates complicated processes like thoughts and memory
(ii) It also plays an essential role in the things your body does without thinking, like blushing, sweating and blinking.
(iii) The nervous system keeps track of what's going on inside and outside of your body and decides how to respond to any situation you are in.

The human nervous system comprises of central nervous system and peripheral nervous system.
(i) The central nervous system consists of brain which narrows into a long tube called the spinal cord.
(ii) The peripheral nervous system consists of cranial nerves from the brain and spinal nerves from the spinal cord.

Parts of Brain
Brain is divided into three parts.
(i) Forebrain
(ii) Midbrain
(iii) Hindbrain

It is behind medulla oblongata. It is the second largest part. Its surface is highly folded. It controls balance and muscle coordination.

1. Brain

• Brain is situated inside a bony cranium i.e. a part of skull.
• Inner to cranium, brain is covered with three protective membranes called meninges.
• Between the inner and middle layers there is a fluid the cerebrospinal fluid which helps to cushion the brain from shock.

2. Spinal Cord
The vertebral column surrounds and protects spinal cord. Like brain, spinal cord is also covered by meninges. Meninges protect spinal cord and also provide nutrients and oxygen to brain tissues through their capillaries.

The peripheral nervous system (PNS) is composed of nerves which link central nervous system with different body parts.
i. Cranial Nerves: Nerves which arise from brain are called cranial nerves.
ii. Spinal Nerves: The nerves which arise from spinal cord are called spinal nerves.
iii. Number of Nerves in PNS: There are 12 pairs of cranial nerves and 31 pairs of spinal nerves in the human body. Some cranial nerves are sensory, some are motor and some are mixed. While all spinal nerves are mixed nerves.

Reflex actions are immediate or automatic and involuntary responses. Reflex actions are also called reflexes. Reflexes are the responses to external and internal environmental changes. Certain responses are without the help of the brain. In this case the spinal cord acts as the control centre. Such a response is a reflex, which involves no conscious control.

Example The nervous pathway for a well-known reflex called the withdrawal of hand on touching hot object.

If we rotate our head fast, the fluid in our ear moves fast too. That is what happens when we first start to feel dizzy. When we stop rotating, our head stops moving but the fluid in the tube of balance organ keeps spinning. So now our brain thinks we are spinning in the opposite direction.

Parasympathetic Nervous System It prepares the body for rest and digestion. Nerves arise from base of brain and tail of spinal cord. It constricts pupil, decrease heart beat and breathing rate, while increase digestion.

Sympathetic Nervous System It prepares the body for emergency conditions that is fight and fight. Nerves arise from middle portion of spinal cord. It dilates pupil, accelerates heart beat and breathing rate while inhibit digestion.

The nervous system helps to coordinate complex and intricate movements of the hand to play a piano or write alphabets. The intention begins in the special area of the brain. The neurons of this area compile a set of information required for an action such as typing or speaking. The information is then transmitted to another area of the brain. It integrates information and ensures that all the muscles work together to produce well-coordinated movements.

Brain The outer region of brain is made of grey matter containing cell bodies and non-myelinated axons. Beneath grey matter is present the white matter consisting of myelinated axons.

Spinal Cord The outer region of spinal cord is made of white matter containing myelinated axons. The central region is made of grey matter, consisting of neuron cell bodies.

Hypothalamus Links the nervous system with endocrine system. Control the secretions of pituitary gland. Control the feelings of rage, pain, pleasure, water balance, thermoregulation.

Hippocampus Formation of new memories.

Medulla oblongata Controls autonomic function like breathing, heartbeat, swallowing and reflexes such as sneezing, coughing and vomiting.

Following major endocrine glands are present in man:
i. Pituitary glands
ii. Thyroid gland
iii. Parathyroid gland
iv. Adrenal gland
v. Pancreas
vi. Gonads

The inner part of adrenal gland, adrenal medulla secretes a hormone called adrenaline in response to stress. It prepares our body to overcome emergency situation. Therefore, adrenaline is also termed as an emergency hormone.

Effects Adrenaline increases the rate and intensity of heart beat, blood pressure and blood flow to the limbs. It is secreted in emotions and anger, hence the face becomes red.

The nervous system uses electrical impulses to send messages through neurons while endocrine glands use hormones to send messages to the target cells through the blood stream.

Each adrenal gland consists of two parts:
(i) Cortex (ii) Medulla
(i) Cortex
Adrenal cortex secretes many hormones called corticosteroids which maintain the balance of salts and water in blood.
(ii) Medulla
Adrenal medulla secretes a hormone called adrenaline. It prepares our body to overcome emergency situation while

Adrenaline and nor-adrenaline are known as fight and flight hormones, because both prepare body for emergency condition. Adrenaline dilates blood vessels in skeletal muscles, heart and brain. Thus increases blood supply which result in high metabolic rate, while nor-adrenaline constricts blood vessels of digestive tract and face. Therefore, we feel hollow stomach and our face becomes white and pale during fear

Hormone Parathormone | Name of Gland: Parathyroid
Hormone: Corticosteroids | Name of Gland: Adrenal cortex
Hormone: Glucagon | Name of Gland: Pancreas

Sensory Nerves i. It contain the axons of sensory neurons only.
ii. It transmit signals to the central nervous system (CNS) from sensory organs (touch, sight, etc. )

Motor Nerves i. Motor nerves contain the axons of motor neurons only.
ii. Motor nerves carry commands from the CNS to muscles and glands for action.

The spinal cord is crucial for reflexes because it acts as a rapid processing center, creating reflex arcs that allow for immediate, involuntary responses to stimuli without waiting for the brain, significantly speeding up protective actions like pulling your hand from heat.

i. These hormones take part in the emergency response of the sympathetic nervous system.
ii. When a person is in emergency, the adrenal medulla releases its hormones to prepare the body for "fight-or-flight" response.
iii. These hormones increase heart rate, blood pressure, blood glucose level, and blood flow to the heart and lungs.
iv. They also stimulate enlargement of bronchioles and dilation of the pupils.

If the pancreas releases too much insulin, blood sugar levels drop too low, a condition called hypoglycemia because the excess insulin causes cells to take up too much glucose, leading to symptoms like shakiness, confusion, sweating and potentially seizures or coma if severe.

An injury to the medulla puts vital involuntary functions at greatest risk. These include the critical centres that control breathing, heart rate, blood pressure and sleep.