Brain Anatomy and Function

Control and Coordination

• Complexity from multicellular organisms increases the distance of cells and organs from each other.
• Organisms require a system to ensure different parts function as a single unit, done through coordination.
• Coordination is required for simple tasks like picking up an object, involving eyes, hands, legs, and vertebral column.
• A comparable mechanism is required for internal bodily functions.
• Changes in the environment that organisms respond to are called stimuli.
• An organism's response to a stimulus often involves movement of a body part.
• Homeostasis involves maintaining constant internal body conditions.
• Homeostasis is derived from 'homeo' (same) and 'stasis' (standing still).
• Plants and animal coordinate and control their functions internally.

Coordination in Plants

• Unlike animals, plants lack a nervous system and use chemical substances called plant hormones or phytohormones for coordination.
• Plant hormones regulate different aspects of plant growth, which can be divided into cell division, cell enlargement, and cell differentiation.
• Plant hormones also control dormancy, breaking of dormancy, stomata control, leaf fall, fruit growth, ripening, and aging.
• There are four major types of plant hormones: auxins, gibberellins, cytokinins, abscisic acid, and ethylene gas.
• Auxins, gibberellins, and cytokinins promote plant growth, while abscisic acid inhibits growth.

Plant Hormones

• Auxins promote cell enlargement, cell differentiation, and fruit growth; responsible for phototropic and geotropic movements.
• Auxin is produced at stem and root tips, moves away from light and towards gravity, and has opposing effects on stem and root growth, synthetic auxins are used in agriculture and horticulture.
• Gibberellins promote cell enlargement, cell differentiation (with auxins), stem elongation, break dormancy in seeds and buds, promote germination, fruit growth, and parthenocarpy induced through gibberellic acid on grape vines.
• Cytokinins promote cell division, break dormancy in seeds and buds, delay leaf aging, promote stomata opening and fruit growth.
• Abscisic acid functions as a growth inhibitor, promotes dormancy in seeds and buds, helps close stomata, promotes wilting and leaf fall, and causes flower and fruit detachment.
• Ethylene gas stimulates fruit ripening, ripening raw fruits occurs faster when they are kept alongside ripe fruit due to the gas released from the ripe fruit, and calcium carbide produces acetylene gas.

Plant Movements

• Plant movements are divided into tropic and nastic.
• Geotropic movement is growth in response to gravity; roots typically show positive geotropism, and stems show negative geotropism.
• Phototropic movement is growth in response to light; stems typically show positive phototropism, while roots show negative phototropism.
• Differential cell division rates caused by auxin result in the stem bending towards light.
• Hydrotropic movement is when roots grow towards a water source.
• Thigmotropic movement is growth in response to touch, seen in climber tendrils; auxin mediates differential cell division.
• Chemotropic movement is in response to a chemical stimulus, positive is growth towards the chemical, growing pollen tubes towards the ovule during fertilization exhibits positive chemotropism.

Nastic Plant Movements

• Nastic movements are independent of the direction of the stimulus.
• Seismonastic or thigmonastic movements occur due to mechanical stimuli like touch; Mimosa pudica leaves droop as water balance in cells changes.
• Photonastic movements are induced by light intensity fluctuations; flowers open or close with changing illumination.
• Thermonastic movements are caused by temperature changes; Mirabilis jalapa blooms in the late afternoon and closes in mid-morning.
• Nyctinastic movements, or 'sleeping movements,' respond to light and temperature, clover and oxalis leaves droop in the evening and rise the next morning.

Control and Coordination in Animals

• The nervous and endocrine systems coordinate control in animals.

The Nervous System

• Nervous system is composed of nervous tissue.
• The nerve cell or neuron is the functional unit.
• It is mainly responsible for complex animal control and coordination.
• Receptors are nerve fiber tips that collect data from the sense organs within animals.
• Phono-receptors in the inner ear handle hearing and balance.
• Photo-receptors in the eye are responsible for visual stimuli.
• Thermo-receptors in the skin are responsible for pain, touch, and heat stimuli.
• Olfactory-receptors in the nose receive smell.
• Gustatory-receptors in the tongue help in taste detection.
• Receptors in sense organs receive stimuli and transmit electrical impulses through sensory nerves to the spinal cord and brain.
• An effector is a body part that responds to stimuli according to the received instructions from the nervous system; effectors are mainly muscles and glands.

Human Nervous System

• The neuron is the structural and functional unit, comprised of dendrites, cyton/soma/cell body, and axon.
• Dendrites receive impulses, the cyton/soma processes impulses, and the axon transmits impulses.
• Axons can be myelinated or non-myelinated and signal transmission is faster in myelinated neurons.
• Schwann cells and the myelin sheath provide insulation and increase impulse speed in the peripheral nervous system.
• Sensory neurons receive signals from sense organs, motor neurons send signals to muscles or glands, and association or relay neurons relay signals between sensory and motor neurons.
• A synapse is the contact point between axon terminals of one neuron and dendrites of another.
• The neuromuscular junction (NMJ) is a point where a muscle fiber meets a motor neuron and carries a nerve impulse from the central nervous system.

Transmission of Nerve Impulses

• Nerve impulses travel from dendrites to the cell body, then to the axon, to nerve endings at the axon tip, and then across the synapse to the dendrite of the next neuron.
• Chemicals are released from the axon tip of a neuron, which crosses synapses or neuromuscular junctions to reach the next cell, acetylcholine is an example of a neurotransmitter.

Organs of the Human Nervous System

• The central nervous system (CNS) encompasses the brain and spinal cord, the brain controls bodily functions, and the spinal cord acts as a relay channel between the brain and peripheral systems.
• The peripheral nervous system is composed of the cranial (12 pairs) and spinal nerves (31 pairs).
• Cranial nerves originate from the brain and connect to organs in the head region.
• Spinal nerves exit the spinal cord and connect to the body's organs, excluding the head region, visceral nerves link internal organs to the spinal cord and the brain.
• The autonomous nervous system consists of a chain of nerve ganglion running along the spinal cord.
• It controls involuntary actions and is divided into the sympathetic and parasympathetic nervous systems.

Sympathetic and Parasympathetic Nervous Systems

• The sympathetic nervous system (SNS) controls the 'fight or flight' response, preparing one to combat or evade perceived threats, and redirects energy distribution.
• Adrenaline released from the adrenal gland causes physiological changes that prepare the body to fight or flee, increasing heart rate and blood pressure to boost oxygenated blood flow to muscles and the brain.
• Responses occur quickly and involuntarily, facilitating rapid reactions to potential threats.
• The parasympathetic nervous system slows organ activity and has a calming effect.
• It helps conserve energy by maintaining stable heart rate and blood pressure, while promoting activities like digestion and sexual function.

Human Brain

• The human brain is highly complex nervous tissue.
• The tissues are folded to maximize surface area in limited space.
• Meninges are layered membranes protect the brain.
• Cerebrospinal fluid (CSF) between the meninges cushions the brain.
• The human brain has three regions: forebrain, midbrain, and hindbrain.
• The forebrain includes the olfactory lobes, cerebrum, and diencephalon.
• The midbrain includes the hypothalamus.
• The hindbrain includes the cerebellum, pons, and medulla oblongata.
• Olfactory Lobes are concerned with the sense of smell.

Cerebrum

• The cerebrum is the largest brain part, divided into right and left hemispheres connected by nerve fibers called the corpus callosum, controls the opposite side of one's body.
• Cerebral hemispheres are composed of an outer cortex (grey matter) and inner medulla (white matter), and contains four lobes: frontal (reasoning and planning), parietal (movement), occipital (visual processing), and temporal (auditory and memory).
• It controls voluntary motor actions.
• It serves as a sensory and perception hub with tactile and auditory facets,.
• It serves as learning and memory hub.

Diencephalon

• The Diencephalon is between the cerebrum and midbrain, linking the nervous and endocrine systems; it sends pituitary gland signals and responses through hormone secretion and has two components.
• The thalamus works as a relay center for pain and pressure.
• The hypothalamus is located at the cerebrum's base which regulates sleep cycles and bodily urges, controls the pituitary gland, body temperature, and blood pressure.
• The midbrain connects the forebrain and hindbrain, is positioned above the pons, and relays neuronal transmissions throughout the body.
• It integrates sensory information from the eyes and ears with muscle movements.
• The hindbrain consists of the pons, medulla oblongata, and cerebellum.
• The structures that control autonomic body systems which govern our heart, breathing, sleep patterns, our bladder function, equilibrium, and control fine motor skills
• The pons relays impulses between the cerebellum, spinal cord, cerebrum and midbrain, which regulates respiration
• The medulla oblongata forms the brain stem with the pons, controls involuntary actions, such as heartbeat or salivation.
• The cerebellum positioned behind the brainstem coordinates motor functions, and ensures motor precision balance and posture are correct.

Spinal Cord

• The spinal cord is part of the central nervous system, it is a pipe-like structure originating from the medulla oblongata.
• Nerve fibres through the vertebral column that are segmented with nerve fibres form the spinal nerves.
• The cross-section shows grey matter surrounded by white matter, the grey matter with a central canal containing cerebrospinal fluid (CSF).
• White matter is made of axons that permit communication between CNS layers.
• The spinal cord links the brain and peripheral nervous system.
• It provides structural support and body posture. Facilitates flexible movements.
• It has myelin, which acts as electrical insulation.
• It transmits signals to the brain.
• It coordinates the body's reflexes.
• Receives and processes all sensory information.

Reflex Actions

• A reflex action is an involuntary movement to avoid sudden danger.
• The reflex arc is the route of nerve signals, in a reflex arc, the flow of signal pathway are as follows: Receptor → Sensory neuron → Relay neuron → Motor neuron → Effector (muscle)
• The receptor is the organ that picks up signals and send them to the sensory neurons relay neuron which are present in the spinal cord.
• The reflex arc passes at the spinal cord-level signals involved in the reflex action that do to send any signals to the brain.
• The brain is protected by being in a fluid filled chamber and enclosed in the cranium.
• The spinal cord is enclosed by the vertebral column. Muscular Movements and Nervous Control are that muscle tissues contain actin and myosin and contracts. when there are triggered series. Calcium enters those cells.
• Contraction in a muscle brings movement in the related organ.

Endocrine System

• The endocrine system consists of endocrine glands that secrete hormones.
• Hormones help the nervous system manage bodily functions (e.g., hunger, mood, reproduction).
• Unlike the nervous system, hormonal control is slower, it can reach areas that neurons do not have access to.
• Hormones are secreted by specialized ductless glands and travel in the blood in very small amounts.
• They act on target tissues or organs, with specificity determined by receptors on target cell surfaces or in the cytoplasm.
• There are about 20 major hormones are released to control.

Glands and Hormones

• Hormone levels vary due to stress, infection, and mineral levels.
• A gland is a cell, tissue, or organ that secretes chemical compounds.
• Endocrine glands secrete hormones directly into the bloodstream such as the pituitary and adrenal glands.
• Exocrine glands secrete via ducts onto a surface like saliva, sweat, and gastric glands.
• Heterocrine (composite) glands have both endocrine and exocrine functions: the pancreas (endocrine) and pancreatic juice (exocrine).
• The hypothalamus is tiny, located near the pituitary gland and links the nervous system.
• Regulating body temperature or homeostasis is a primary duty of this,
• Further, body weight, heart weight, or one's circadian rhythm is regulated through these hormones.

Pituitary Gland

• It is a pea-sized gland located at the base of the brain.
• It is the master gland that secretes all other hormone's glands.
• Secretion over or reduces growth-hormone (GH) release.
• Dwarfism result due to lacking amounts, or in other instances, acromegly, or gigantism may emerge.
• Thyroid stimulate production, FSH, LH, and melanocyte release as hormones within this gland are activated.

Thyroid Gland

• Butterfly shapes, secretes thyroxine around the throat.
• Hormones will affect their metabolic rate and bone or nervous system growth or development.
• Iodine synthesizes thyroid hormone,
• Under producing thyroxine due to lacking iodine result to goiter, or enlarged necks, resulting from that deficiency iodine, cretenism and mental growth.

Parathyroid Gland

• The parathyroid gland is what regulates the calcium and phosphorus in bone.
• The pineal has melatonin release for sleep regulation. The pancreas has a leaf like gland, which creates digestive hormones.
• The pancreas can generate glucagon and produce sugar levels. Those proteins, carbohydrates, or lipids are released by exocrinization. A failure within there can trigger diabetes.
• The adrenal has pairs or each kidney. The pair can release cortisol or lower stress from the hormones.
• Over reacting could lead to adrenal or blood increases by pressure.
• If epinephrine is discharged in the nervous system, it may trigger stress rapidly, cause the body to react, or trigger blood flow or heart rate increase.

Hormones Continued

• Norepinephrine hormones react with other hormone like functions can create mobilization or neural response.
• The Thymus can activate secretion within hormone.
• The gonads testes that produce hormone within testerone activate male or female gonads.
• Estrogen produces gonads or sexuality in female and male reproduction or progesterone or pregnancy can come from this hormones.
• Hormones release hormones with feedback mechanics. Releasing hormones are in the built and for amounts. Glucose in blood are in insulin activation and release for the increase so it can normalize to homeostasis effectively.
• Releasing that and stimulating secretion or breaking to support it is good with that mechanic is sustained efficiently

Test your knowledge of brain structures and their functions, covering roles from sensory relay to motor control and autonomic regulation. This quiz explores the midbrain, medulla oblongata, pons and the interplay between nervous and endocrine systems.