Coordination and Response in Plants and Animals The Structure and Function of the Brain

Receptors, Effectors and the Central Nervous System Syllabus Objectives Describe the functions of the main region of the brain Identify the main sense organs and the stimuli to which they respond

Introduction The brain and spinal cord receive impulses and pass them on to effectors The overall function of the brain is to Coordinate and control the activities of the body It controls all body functions except those under the control of simple spinal reflexes Size: 1.5 kg Protected by outer membranes, a layer of fluid and the bony skull

The Human Brain The brain is divided in 3 main parts Cerebrum Cerebellum Medulla / medulla oblongata

Cerebrum Largest part of the brain Thin outer grey matter (3 mm deep) – cerebral cortex Contains deeply packed relay neurons cell bodies of motor neurons endings of sensory neurons

Cerebrum cont’d The thick inner white matter is made up of nerve fibres (axon and dendrons) The cortex is highly folded with deep grooves One groove divides the cerebrum into right and left hemispheres Folding increases the surface area of grey matter More nerve cells and synapses allow more complex behavioural patterns

Cerebrum cont’d Control of all voluntary actions take place here It is also the center of sensory awareness Other things controlled here: Memory Reasoning Judgment Intelligence Speech and language

Cerebrum summary The cortex is made up of sensory areas, which receive impulses from receptors motor areas where impulses going to effectors originate Association areas that Interpret Integrate Store information

Cerebellum Located beneath the posterior end of the cerebrum Receives information from the ear and muscles about posture and balance Controls Walking Running (in birds it is large and controls flying)

Medulla/Medulla Oblongata Located below the cerebellum and merges with the spinal cord Controls many unconscious processes/involuntary actions Regulation of body temperature Blood pressure Breathing Heart rate Swallowing Vomiting Coughing Yawning

Medulla/Medulla Oblongata cont’d It controls the autonomic nervous system which regulates internal activities of which the individual is not aware e.g. activities of the sweat glands, muscles in the gut, blood vessels and heart, reproductive tract receives motor fibres from the autonomic nervous system (ANS)

Autonomic Nervous System (ANS) Made up of 2 parts Sympathetic nervous system Parasympathetic nervous system Most internal organs receive fibres from both systems Their actions are antagonistic Sympathetic stimulation causes an increase in heart rate; parasympathetic stimulation causes a decrease in heart rate

Hypothalamus Situated underneath the front part of the cerebrum. It is the main control center for the ANS Centers in the hypothalamus regulates the body activities concerned with homeostasis It also controls the release of hormones from the pituitary gland

Homeostasis Various processes that operate within an organism to maintain a constant internal environment Information on the state of a particular internal factor is sent to the hypothalamus When a change from the norm occurs mechanisms are put in place to oppose the change – negative feedback Homeostatic responses are either through nervous system, actions of hormones or both